Are the new save files supported in an older version of the game?

No.

No!

So once you switch version, you can't load them in an old version anymore.

So if you do switch to experimental, we highly recommend that you stay on that version.

And if you still want to be able to switch back to an older version, then you have to back up your saves.

So what do I need to do?

So you shouldn't really need to do anything out of the ordinary.

You can still load up and save the game as usual.

and everything should be dandy.