I can't believe those numbnuts at legal shot you down, Jackson. Even someone with a blindfold could see that your designs are phenomenal.
Sure, they're phenomenal, but unfortunately they actually have a legitimate reason for prohibiting alterations of the Rider Back. As a 120-year-old back design (first printing was 1893), any protection it may have had from copyright law went out the window a long time ago. This leaves USPC to prevent people from duplicating their work by defending it under trademark law, as it is one of their more ubiquitous deck backs.
For such a defense to hold water, however, they can't allow the trademark to become "diluted" by permitting alterations to it. USPC Legal came down with this decree over two years ago - no alterations to the assorted trademarks of the company, including the Rider Back.
Also forbidden are any of their "standard" backs such as the Bee Diamond Back, etc., and any of their unique jokers or Aces of Spades. Even the Mandolin Backs and Maiden Backs can't use an altered version of their jokers and Aces of Spades, though you can replace them entirely with different designs.
I have several Ellusionist gaff cards for decks like the Bicycle red/blue, Ghost, etc. that will no longer be reprinted as a result of that ruling, and it was among the many reasons that Ellusionist drifted away from Bicycle-branded products and created more of their own designs. Those decks were meant to share nearly the same gaffs with the Black Tigers - the video "Army of 52" covers using the gaffs in all of those decks because most are shared throughout the gaffs for them - but my new Black Tigers gaffs are either missing some of the old cards or have redesigned newer versions of them that don't infringe on the trademark.