It suddenly occurs to me that now that you have a new STA reference etc. What if a friend near you (or one of us) were to write to the palace asking about "our friend's kilt whose tartan is so very similar to, but registered differently from the restricted tartan" and asking if the palace minded him wearing it.

They wouldn't recognize it as the same correspondent so they would have to think from square one. I'm betting you would shortly have absolute permission to wear the kilt.