I don't own an Apple Watch (yet). So I don't have any direct experience with UV cured screen protectors on an Apple Watch.
I have used them quite successfully on several smartphones, however. I assume the process is similar.
I'm familiar with Whitestone Dome because that is the brand that I've used. They do come off, but it does take a bit of force to remove it. I recommend finding something somewhat flexible, but non-scratching, to pry the screen protector off. Something like a plastic credit card would work.
When I've had to remove them because of damage, I've just lifted off a corner with a fingernail and then slowly worked the rest off using some flexible piece of plastic. Any residue can be cleaned off with an alcohol wipe.