it should change the way it feels
I suggest not to use Fanning Powder unless its a horrible horrible deck, or a really old tattered deck, or a manipulation deck. Its not the most pleasant of feels.
Although it works, it doesnt feel... "soft" anymore
No, it won't change it, because the way fanning powder is intended to work, is that the dimples on the cards hold the powder, plastic cards, generally don't have dimples, but if they do, then yes it will work. Also bear in mind, non-dimpled cards will be slightly affected by the powder but not considerably.