Hey there @Achaius! From what I understand, the owner of this thread is on indefinite hiatus, so I hope you don't mind if I answer your question.

1. Decorative Item Potions are able to find all decorative items, so fortunately, this includes wall skins and wall covers!

2. For the Item Rarity Excluder, if your question is just about whether or not it can find wall skins, the answer is yes. If you want to use it to raise your chances of finding a particular wall skin, this can be easy or hard depending on the rarity of the wall skin. If the rarity is between 1% and 33%, then you can just make a g100 rarity excluder and not worry about doing any math. But if the rarity is beyond 33%, then you have to make a lower grade excluder in order to widen the scope of rarities it can find. Sadly I don't know the math for this; I only understand the basic concept. But I hope I've helped in some way. ^^