My application is beginning to interest prospective clients.  This may be
wishful thinking, but if I have a lot of clients how will I update a
production backend when I need to add tables (for example, for new
functionality in the new release front end) or modify tables with fields.

The clients I talk to generally do not allow executables to be installed on
user PCs.  So an executable to do this is out of the question.   If by some
miracle I have 50 or more clients, how am I going to accomplish adding new
tables to the production backend or adding a field to an existing table.  I
don't want to have to accept each backend one by one and do the changes.
Code is the answer, but how to best implement this.

Of course, before anything is done, backup, backup, backup.....

Advice, suggestions experience on how to best accomplish this is appreciated.

Thanks.