we do it similarly, though we intentionally picked numbers close to each other for just this reason (can't afford another bike) 801, 811

we use yellow or white duct tape for the plate color around the number, and doctor the number from 0 -> 1 -> 0 with black electrical tape.

changes easily between races and keeps 3M in business :?

Harder to envision if the numbers are vastly different, but can be done -

I like the velcro idea