Is it possible to redeem Ubisoft Store's 20% discount with U100 on the PlayStation Store or apply for a discount?

E.g. Apply for a rebate on Ubisoft Homepage and redeem / charge code sent there while shopping or pre-ordering at the PlayStation Store.

Try it. What have you got to lose? You do not use the U-Coins anyway. I have 2328 of them unused and have in the games pretty much everything I need to buy.

Unfortunately, I can't test it for you because I have only one PC, but I would not see any reason why it should not work, because the store is indeed quite the same across platforms (up to the overlay and the game versions maybe)

edit: You can only use the promo code for games that do not have a discount.