You would think it would be possible to just swap out the currency mechanism and not the entire machine. Seems like there’s an opportunity there somewhere…

Alternately, get a bill exchanger. New bill goes in, old bill comes out.

Depending on the age of the machine, you could maybe just update the firmware. I mean, what’s it comparing the bills put into the machine to? Data hardwired into it or a file stored somewhere that can be changed?