If I made a copy of an apps google sheet and changed the name of the copy, will the app still connect to that copy of the google sheet or only the original?
The below only applies to Google Sheets spreadsheets.
Once the app is connected to the Google Sheets spreadsheet, the app no longer cares what the name of the file is; instead, it users a Google-internal identifier to access the file. This means you can rename the Google Sheets spreadsheet with no affect on the app’s ability to get to it.
Creating a copy of a Google Sheets spreadsheet used by an app has no affect on the app’s ability to get to the original spreadsheet. You could even give the copy the same name as the original and the app would continue to use the original.
The above only applies to Google Sheets spreadsheets.
I only use Google Sheets spreadsheets, so I can’t say how other data sources might behave.
So if I have a client who plays around with the copy of the google sheets the app and the original google sheets won’t be affected?
Correct: a user of the copy will have no affect on the app.