I don't see why not. I've received many cards where someone has added glitter or cotton.
You might want to search for my 3-D cards which are layered cards (store bought) in fact my cards this year are like that I usually do a stamped card.

See instructions for making 3 D cards
Also check out the gallery for this forum back to Feb 2005 and there is a photo of one of my cards.

Here is a link that might be useful: 3 - D Cards

Marie, you can't tell me you aren't talented enough to start from scratch, if you can embellish a store bought card! I can make them with rubber stamps, but not embellish store bought! You don't have to be talented to make them from scratch! It could be as simple as white card stock cut in half then folded in half, with one rubber stamp and colored ink out side, a Merry Christmas or Happy Holidays stamp on the inside and sign your name! Is there somewher you can take a beginning rubber stamp class?

Tami

You are getting right into the hottest thing right now - Altered Art! By adding stickers, 3-D elements, etc. you are "altering" your cards. Very hot right now!!