So if you are trying to do this widely, the first thing I recommend considering is making a public app. The cost is $50/month and it has anonymous users.
I do not think that is what you are looking for but just in case. What I recommend is if you are wanting to do and work on upgrades for an app then making a copy of the app editing it when it is not pushed out live then going here to upgrade the app version.
Here you can upgrade the app once it has already been created because you do not want to be editing the back end while users are working on it.
If you give customers their own sheets then it is technically different apps that they would have. So making a copy of that app would be what you are doing but you cannot upgrade them all at once. Copies can be made in the others tab.