You will never need this quest so no need to worry about it.
When the game first came out, it was possible for Man/Elf to buy a pony by mistake and for Dwarf/Hobbit to buy a Horse. Since you could not ride the mount if you made this mistake, this quest was provided to allow you to trade your original mount token (took up pack space) for a different one.
When they changed the mounts to be stored as skills, this situation can not happen any more since you buy a Steed and receive either a horse or pony depending on your race.
[CENTER][B][I][COLOR=yellow]LOTRO proves that Middle Earth is Hobbit Forming![/COLOR][/I][/B][/CENTER]