10ofclubs: USPC doesn't allow for the alteration of the Bicycle Rider Back, Ace of Spades and Jokers. Everything else is fair game. Even on the Maiden and Mandolin Backs as well as the Rider Backs, they still don't allow alterations of the AoS or Jokers - but they do allow replacements with alternate designs. So there's still a lot of room in which to work, as regards the Rider Back playing cards, just nothing that involves changing elements of the back, like a Twilight Angels gaff card or a marked deck.
Chisari: Since when does USPC get hot and bothered about that? If it's a custom-designed deck, they have no objections. In fact, they've been in some cases INSISTING that the company making the design take the credit for it on the box. If you look at some Ellusionist decks that still are and have long been in print, where the sides used to say "U.S. Playing Card Company", the most current printings of them now say "Ellusionist Playing Card Company" instead.