Could Biden stand as acting President and Pelosi as acting Vice President until an Amendment passed?
I'm not a constitutional lawyer, so it would probably have to go to the SC. I'm guessing your scenario would be the case except I don't see how they could change the constitution and make it retroactive.
And the legal beagles would argue about it. That is a given.
I know you can pass some things retroactively, but laws, I doubt. I think that is what habeus corpus means. Better look it up, remember learning about it in school that you couldn't change the law and retry a criminal. It's a little different than double jeopardy, but don't take my word for any of this.