Blockstates conversion, update all modded blocks on start?

[Kikoz]

Hello, I'm trying to make all of the modded blocks to update their states once, or have a conversion for the blockstates. Meaning I have a saved world with the old blockstates, and now in the newer update on which I'm working the states have been changed to work the same but more effective (lower state count).

Basically so players could just update to the newer version and their stuff would not break just update/convert...

What would be the best approach for this?

 

[Kikoz]

For example the previous states were four booleans (North,East...) and now I removed those and made a part enum which has 3 parts ( single, left, right ). And now as that changed I would like the already placed blocks in older versions to update in the newer version, Thanks!