If you're worried about affecting the collector value by removing and
restoring the number plate, take some good photos of the plate and tractor before you remove it, and keep them in your file with other reciepts. If you're not presenting this to a seller as a rare, one-of-a-kind tractor, they likely won't care, and if they do, you have
Also, it's not like Super As are so rare that a removed-and-replaced
number plate will halve its value.
Perhaps you can get a salvage plate (with the painted script) from someone parting out a Super A, and give that to your decal maker.