The best you can hope for is to load the save state from the previous core version and work your way to an area that allows for a normal memory save. Afterwards, update the core load the save and make a new save state. I realize this wouldn't be possible for all games and it's a major hassle, but it's really the only option. It's best to only utilize save states for very casual use and at no time when it's crucial to keep them for long periods of time. Save state formats can change at any time depending on development. You might see an emulator/core keep its format throughout its lifespan, or you might see it change several times a year.
