How much later? Cryptographic systems certainly have methods for allowing revoting up to a deadline, but endlessly mutable voting is insane. It's also not really any different from today. I can say I didn't vote for candidate A 12 months after the upcoming election and it means... well... nothing.
You can do A' in some US states... you can vote by mail/early vote, and then later request they spoil that ballot and do it again, or by voting on election day the mail-in is invalidated.
There is no "US voting system". Each of the 50 States have their own systems, often several systems, and where there are several systems it's the counties that pick a system that suits them.
I'm confused. Can you explain the exact issues created by this repudiation system practiced by US states? Maybe there's a real issue that hasn't been addressed that I am unaware of.