Harvey,
If I understand it correctly, then you have another 99 forecast files for the supervisor? One for each of the main forecasts? Doing this seems like it just doubles your problems.
With my limited understanding, the only solution I see is to have the user close their forecast file and then the supervisor can open it and make changes. When the super is done, then the user can open it and continue.
The only other way is to open the files in shared mode and if you are going to do this, then you don't need separate files for the supervisor. This might be accomplished without making the app a complete multi-user app, by only allowing one worker and one supervisor access to one forecast (at the same time). And when the super has access, then the worker cannot make updates. This would be done via a control record or file of some kind. How difficult this might be to accomplish depends on how your code is written.
Now, or years from now, you are probably going to have to address the multiuser issue. It always takes less work to do it sooner since your app inevitably gets more complicated as time goes on.
Regards,
James