As of 2.4 , i've noticed that you get prompted now when buying Honor Items [i.e. You are about to purchase item x, are you sure yes/no] . I always fill up on the pots you buy with AV marks [i always lose AV marks as can only carry 100] and was pretty annoyed to click through it 20 times for my pots.
Anyhow i think that measure is there to ensure you don't buy the wrong stuff.
As for exchanging gear, i'm sure they'll do it if it was a mistake. But just because you figured out Feral and PvP does not go together [compared to Resto] does not mean they will change your gear.
However, as a druid, i see no reason why you can't keep your feral set and get a Balance set -anyway- . It's the fate of a druid to grind for multiple sets [because you can] of gear. I grinded for a full Dragonhide [feral] set AND i grinded for a Resto set [kodohide], AND i'll probably grind for a Balance set too......and i feel no reason to want to give up or switch any of the sets.
The PvP Feral set is pretty damn good for PvE tanking/dps'ing all the way to SSC/TK. I STILL wear the Dragonhide Spaulders on my tanking set.
I only have 20 slots of bagspace ...that's life of a druid.
The new changes to nurturing instinct [that funny healing talent in the feral tree] , made it alot easier to heal in your dps set [or any set with lots of agility] , so it's -always- worth it to have a good feral set.
Also the changes to spirit [increasing mana regen] , made it so that i can put on my spirit-based healing set with a feral spec and get insane regen without being in tree form [i'd go as far as saying i can regen now in caster form as much as i did in tree form pre-2.4 ]