When renaming a column, change the name in the spreadsheet, manually change the name in the app editor, then regenerate columns. This will preserve the column’s configuration. Note that AppSheet won’t care that the column name in the spreadsheet and the column name in the app don’t match until you do a regenerate. You can even save with the name mismatch and AppSheet won’t care. AppSheet accesses column data by column number, not column name; the names are just to setup the mapping.
You could copy the app and make your changes in the copy. When done and working, copy back to the original. This is cumbersome because you’ve potentially got a large set of changes that may take a long time.
You could copy the app, make one change in the copy, see what breaks and what’s needed to fix, then make the change in the original, knowing what to expect. Good if you want to make incremental changes during a well-defined maintenance window.
You could add a column of the new name to the app, migrate to the new column, blank the old column in the spreadsheet and regenerate columns. This approach keeps the app working with the old column as you migrate and for users that haven’t synced recently.