It may be possible. You might set up two accounts, each with a different privilege set for the same users. A script could use Re-LogIn to automatically log the user in under a different account name/privilege set when moving to a different part of the system.
Or you could define privilege sets that combine permissions for multiple groups to use with users that are members of more than one group.
One Data file
Multiple interface files for various business needs such as:
I'm familiar with the data separation concept, but such a large number of Multiple interface files instead of a single interface file would seem to complicate the design, maintenance and management of your database by quite a bit for little gain over using a single interface file.
If you were doing a Database for over 150+ users with over 30+ different permission sets. What method would you go about making this happen the easiest and most manageable way.
Easiest would be a long way from easy. Without putting on my consultant hat and making a detailed survey of your database, your user base and how they need to work with the database, it would be hard to say and the final solution may also use external server authentication.