Sounds quite OP to me.
Whats next? Make it possible to equip 2 horses and switch between an arabian and a destrier while riding?
Tell you what, if you're able to ride 1 horse with another in your backpack under current crpg rules and restrictions without hacking, then by god yes you may switch between those 2 horses since you're so awesome I cannot comprehend the amount of awesomeness you hold.
Its a bad analogy though since archers are able to take 2 different kind of arrows right now under current slot restrictions but are unable to decide which kind of arrows they want to use. Its just giving them the ability to pick which one they can use, just like throwing is able to.