Can a scratched Apple Watch face be replaced?

Not really. Apple doesn't replace the screen on Apple Watch. The prices in the link Randy-12 provided would be you handover a wiped Apple Watch and they replace it likely with a refurbished watch. Instead of paying for the high cost, I'd suggest a good screen protector for your watch, which would likely hide the scratches you have and prevent new ones.

Yes see https://support.apple.com/watch/repair/service