I have a stable app I copied to make improvements. Now that my improved prototype is stable, I want to link the first google sheet to my new improved app. Is that possible and how can I achieve that?
Yes, however if the improvements included column additions or removals, you want to make sure the original sheet(s) have had the same updates.
Once you are comfortable with that, then you would need to go into each Table in the app, Storage section and change the Source Path and Worksheet Name. If you have a lot of tables, this can get tedious.
You could also simply copy the data from the original sheet into your improved version.