Only if it's rainbow.
I think if you choose the rainbow option you can dispense with the bow. It'd be kind of redundant. :)
I'm guessing that I don't have to wear the pony's tale...
No, you don't have to - although if you cut off Rainbow Dash's tale and wore that it WOULD be acceptable.
Where should this comment appear?
This pairing only
Whenever "Have a donkey's tail" appears
Whenever "Have a long, luxurious pony's tail that's permanently decorated with ..." appears