A friend of mine has smaller hands than mine (shorter and thicker), and he had a smaller bass box made for his Regal (later model Regal. I have one too. Possibly a Weltmeister knockoff).
Another friend of mine built it for him. You don't need to get the current one refitted. You could get an alternate one constructed, screw that one on, and when you're ready to sell the box, put the old one back on.
Just have to find someone to make you one. I've never made one. I think the hardest part would be fitting the baffles and dividers in the inside, not the construction of the outer frame.