There are a few issues with Centaur's tooltips, mainly in Return and Stampede. Besides the issues, there are more things that could be improved.

As always I prepared something and here are the changes I did

Hoof Stomp:
* No changes.

Double Edge:
* Added radius to traits
* Reworded the ALT note for consistent wording

Return:
* Changed status buff name from "Return" to "Return Aura", and gave it a description
* Changed default description so that it is clear that it only affects Centaur himself.
* Once the talent is chosen, the following happens:
** Ability name changes to "Return Aura"
** Description changes to reflect it now being an aura and affecting nearby allied heroes as well as Centaur
** A radius trait appears

Stampede:
* Added damage type to header (note: doing this will also require adding "CalculateSpellDamageTooltip: 0" to "damage_reduction_tooltip_scepter" and removing it from "strength_damage")
* Reworded description for consistent wording.
* Added slow value to the traits
* Reworded aghs description, so that it says allies destroy trees.
* Removed redundant note about spell immunity (info already in the header)
* Moved "each enemy can be trampled once" from description to an ALT note
* Added ALT note saying only player-controlled units are buffed
* Added ALT note clarifying who gets creditted for the trample damage
* Reworded Stampede's buff description for consistency
* Stampede's buff now updates upon acquiring Aghanim's Scepter, and starts mentioning the 40% damage reduction
* Renamed Stampede's debuff on enemies from "Stampede" to "Stampede Slow", and reworded it for consistency

Note: The changes to Return's tooltip, and to Stampede's buff are currently impossible to implement without replacing abilities/modifiers (which would be a bad solution), since tooltips are not this flexible currently. There is no way to make talents or aghs replace descriptions or names. It would be really nice if they were, though.

Image comparing the changes to the current tooltips
Spoiler: 


And here are the modified dota_english.txt and npc_abilities.txt

Code:
		"DOTA_Tooltip_ability_centaur_hoof_stomp"								"Hoof Stomp"
		"DOTA_Tooltip_ability_centaur_hoof_stomp_Description"					"Slams the ground, stunning and damaging nearby enemy units."
		"DOTA_Tooltip_ability_centaur_hoof_stomp_Lore"							"When the mighty hoof of the Warrunner touches soil, the tremors are felt far and wide."
		"DOTA_Tooltip_ability_centaur_hoof_stomp_radius"						"RADIUS:"
		"DOTA_Tooltip_ability_centaur_hoof_stomp_stun_duration"					"STUN DURATION"
		"DOTA_Tooltip_ability_centaur_hoof_stomp_stomp_damage"					"STOMP DAMAGE:"
		"DOTA_Tooltip_ability_centaur_double_edge"								"Double Edge"
		"DOTA_Tooltip_ability_centaur_double_edge_Description"					"Centaur strikes a mighty blow at melee range, damaging both himself and a small area around the target. Centaur cannot die from Double Edge."
		"DOTA_Tooltip_ability_centaur_double_edge_Lore"							"In the spurs of combat, Bradwarden's vicious strikes sometimes cause self-inflicted collateral damage."
		"DOTA_Tooltip_ability_centaur_double_edge_Note0"						"Deals magical damage to the targets and the caster."
		"DOTA_Tooltip_ability_centaur_double_edge_edge_damage"					"DAMAGE:"
		"DOTA_Tooltip_ability_centaur_double_edge_radius"						"RADIUS:"
		"DOTA_Tooltip_ability_centaur_return"									"Return"
		"DOTA_Tooltip_ability_centaur_return_alt"									"Return Aura" -- should replace the above name upon choosing the talent
		"DOTA_Tooltip_ability_centaur_return_Description"						"Centaur counters every attack, damaging the attacker based on a percentage of his own strength."
		"DOTA_Tooltip_ability_centaur_return_Description_alt"						"Centaur and all nearby allied heroes counter every attack, damaging their attackers based on a percentage of Centaur's strength." -- should replace the above text upon choosing the talent
		"DOTA_Tooltip_ability_centaur_return_Lore"								"Bradwarden has no need to parry his opponent's attacks; his armor-like hide does it for him."
		"DOTA_Tooltip_ability_centaur_return_Note0"								"Return triggers on every successful attack."
		"DOTA_Tooltip_ability_centaur_return_Note1"								"Return deals damage to towers."
		"DOTA_Tooltip_ability_centaur_return_return_damage"						"DAMAGE:"
		"DOTA_Tooltip_ability_centaur_return_strength_pct"						"%STRENGTH BONUS DAMAGE:"
		"DOTA_Tooltip_ability_centaur_return_aura_radius"						"AURA RADIUS:" -- should only appear upon choosing the talent
		"DOTA_Tooltip_ability_centaur_stampede"									"Stampede"
		"DOTA_Tooltip_ability_centaur_stampede_Description"						"Centaur leads all allies into a vicious charge, allowing them to move through units at max speed. While charging, any enemy coming too close to allies get trampled, getting slowed and taking damage based on Centaur's strength.\n\nUpgradable by Aghanim's Scepter."
		"DOTA_Tooltip_ability_centaur_stampede_Lore"							"The great belt of Omexe, which labels Bradwarden as the greatest warrior of his kind, incites his fellow gladiators to follow him into barbarous combat."
		"DOTA_Tooltip_ability_centaur_stampede_Note0"							"Affects all player controlled allies. Does not affect lane creeps."
		"DOTA_Tooltip_ability_centaur_stampede_Note1"							"Trample damage is creditted to the trampling units."
		"DOTA_Tooltip_ability_centaur_stampede_Note2"							"A unit can only be trampled once."
		"DOTA_Tooltip_ability_centaur_stampede_radius"							"TRAMPLE RADIUS:"
		"DOTA_Tooltip_ability_centaur_stampede_duration"						"STAMPEDE DURATION:"
		"DOTA_Tooltip_ability_centaur_stampede_strength_damage"					"STRENGTH MULTIPLIER DAMAGE:"
		"DOTA_Tooltip_ability_centaur_stampede_slow_movement_speed"				"%MOVE SPEED SLOW:"
		"DOTA_Tooltip_ability_centaur_stampede_slow_duration"					"SLOW DURATION:"
		"DOTA_Tooltip_ability_centaur_stampede_damage_reduction_tooltip_scepter"		"%SCEPTER DAMAGE REDUCTION:"
		"DOTA_Tooltip_ability_centaur_stampede_aghanim_description"				"Heroes affected by Stampede take reduced damage, are able to run through cliffs and destroy trees in their path."
		"npc_dota_hero_centaur_bio"												"It's said that a centaur's road is paved with the corpses of the fallen.  For the one called Warrunner, it has been a long road indeed.  To outsiders, the four-legged clans of Druud are often mistaken for simple, brutish creatures.  Their language has no written form; their culture lacks pictographic traditions, structured music, formalized religion.  For centaurs, combat is the perfect articulation of thought, the highest expression of self.  If killing is an art among centaurs, then Bradwarden the Warrunner is their greatest artist.  He rose to dominance on the proving grounds of Omexe, an ancient arena where centaur clans have for millennia gathered to perform their gladiatorial rites.  As his fame spread, spectators came from far and wide to see the great centaur in action.  Always the first to step into the arena, and the last to leave, he composes a masterpiece in each guttering spray, each thrust of blood-slickened blade-length.  It is the poetry of blood on steel, flung in complex patterns across the pale sands of the killing floor.
Warrunner defeated warrior after warrior, until the arena boomed with the cheering of his name, and he found himself alone, the uncontested champion of his kind.  The great belt of Omexe was bestowed, wrapped around his broad torso, but in his victory, the death-artist found only emptiness.  For what is a warrior without a challenge?  The great centaur galloped out of Omexe that day with a new goal.  To his people, Warrunner is the greatest warrior to ever step into the arena.  Now he has set out to prove he is the greatest fighter who has ever lived."

		"DOTA_Tooltip_modifier_centaur_return" 								"Return Aura"
		"DOTA_Tooltip_modifier_centaur_return_description"					"Countering every attack, damaging the attacker based on a percentage of Centaur's strength."
		"DOTA_Tooltip_modifier_centaur_stampede"							"Stampede"
		"DOTA_Tooltip_modifier_centaur_stampede_Description"				"Phased, hasted, and damaging and slowing enemy units upon trampling them."
		"DOTA_Tooltip_modifier_centaur_stampede_Description"				"Phased, hasted, taking %dMODIFIER_PROPERTY_INCOMING_DAMAGE_PERCENTAGE%%% less damage, and damaging and slowing enemy units upon trampling them." -- should replace the above text upon choosing the talent
		"DOTA_Tooltip_modifier_centaur_stampede_slow"						"Stampede Slow"
		"DOTA_Tooltip_modifier_centaur_stampede_slow_Description"			"Movement speed slowed by %dMODIFIER_PROPERTY_MOVESPEED_BONUS_PERCENTAGE%%%."
Code:
	//=================================================================================================================
	// Centaur: Stampede
	//=================================================================================================================
	"centaur_stampede"
	{
		// General
		//-------------------------------------------------------------------------------------------------------------
		"ID"							"5517"														// unique ID number for this ability.  Do not change this once established or it will invalidate collected stats.
		"AbilityBehavior"				"DOTA_ABILITY_BEHAVIOR_NO_TARGET | DOTA_ABILITY_BEHAVIOR_IMMEDIATE"
		"AbilityType"					"DOTA_ABILITY_TYPE_ULTIMATE"
		"SpellImmunityType"				"SPELL_IMMUNITY_ENEMIES_NO"
		"SpellDispellableType"			"SPELL_DISPELLABLE_NO"
		"AbilityUnitDamageType"			"DAMAGE_TYPE_MAGICAL"
		"FightRecapLevel"				"2"
		"AbilitySound"					"Hero_Centaur.Stampede"

		"HasScepterUpgrade"			"1"

		// Time		
		//-------------------------------------------------------------------------------------------------------------
		"AbilityCooldown"				"90.0 75.0 60.0"

		// Cost
		//-------------------------------------------------------------------------------------------------------------
		"AbilityManaCost"				"100"

		// Stats
		//-------------------------------------------------------------------------------------------------------------
		"AbilityModifierSupportValue"	"0.2"	// hits everything on the map

		// Special
		//-------------------------------------------------------------------------------------------------------------
		"AbilitySpecial"
		{
			"01"
			{
				"var_type"			"FIELD_FLOAT"
				"duration"			"4.0"
			}
			"02"
			{
				"var_type"			"FIELD_INTEGER"
				"base_damage"		"0"
			}
			"03"
			{
				"var_type"			"FIELD_FLOAT"
				"strength_damage"	"1.0 2.0 3.0"
			}
			"04"
			{
				"var_type"			"FIELD_FLOAT"
				"slow_duration"		"1.8"
			}
			"05"
			{
				"var_type"			"FIELD_INTEGER"
				"radius"			"105"
			}
			"06"
			{
				"var_type"			"FIELD_INTEGER"
				"slow_movement_speed"			"100"
			}
			"07"
			{
				"var_type"			"FIELD_INTEGER"
				"cooldown_scepter"			"90 75 60"
			}
			"08"
			{
				"var_type"			"FIELD_INTEGER"
				"damage_reduction"	"40"
			}
			"09"
			{
				"var_type"			"FIELD_INTEGER"
				"damage_reduction_tooltip_scepter"	"40"
				"CalculateSpellDamageTooltip"		"0"
			}
		}
	}