Hi Lee and all, I have spent a good part of a day updating all my assets into new folders. Why you ask?!
Now I can see on updates a few areas get updated and can override these changes.

Is it possible to have an option to only update areas you want like the app system core files and not all the entities, script, folder structure, etc?

So steam will offer this option and a list of which items need to be updated for best performance as I don't want to keep changing this each time. I know I can rename and make new folders for the older version but have reconfigured loads of scripts, AI's, models, textures, etc.

Any help would be appreciated... thanks in advance.

Steam does not offer this, I think. But I know your problem and my solution is a complete copy of the hole game guru files and I just copy over all files excluded the files folder. I know this need a lot of space, but I need a development area without any updates which can cause errors, for my game.