This is a good idea---ask first. I'm loving that bag too!!! I hope you get it!!!There's no guarantee that it would work and I think it largely depends on the relationship you have with your SAs. The PCE coupons say that they are not good on previous purchases so it's possible that they wouldn't allow it. Maybe you should ask your favorite SA ahead of time. I think if it was a week or two before PCE that you wouldn't have a problem but a couple months before -- I don't know.
I asked my favorite SA and he said they probably will since I have a good standing relationship with the store.
If not I will return it!!! If they do give me the difference I might just ask for it in a store credit so I can get something else. I think I am offically banned though!!
I'm sure they would. Good luck with not wearing it. Just knowing I have a new bag I must use it.