You seem to forget the order if succession wasn't part of the constitutional amendments until after JFK was assassinated. You can do as much alternate history as you want, even become a prize winning alternate history series author like Harry Turtledove (South won the Civil War) ir Eric Flint and co authors changing European history from 1632 on, but it is still fantasy, fiction, make believe.
History gets rewritten all the time. Memories are faulty and biased. As primary, secondary and tertiary witnesses die and materials degrade are misplaced or lost and technology becomes outdated, the fine details if history get lost. Those of us who were in our teens and early twenties during the Apollo MANNED moon landings and 9 years old during the Cuban Missile Crisis are now in our 60s and 70s. We are DYING. Our legacies live on in the memories of the people whose lives we touched, but their memories are selective and can be inaccurate, altered because of trauma. "Truth" is SUBJECTIVE.