Happy Happy, Joy Joy!
Last night I was finally able to get IL2-MAT Manager
to work in Windows VISTA. Unfortunately, to make this happen I had to completely uninstall IL-2 Sturmovik 1946 and then reinstall it outside of VISTA's "Program Files" folder. After that, I reinstalled IL2-MAT Manager outside of the Program Files folder as well. Doing this now allows both programs to update their various configuration files when changes are made. It seems that VISTA is naturally overprotective of anything located in the Program Files folder.
Similarly, a few nights ago I achieved success with installing Uber-Quick Mission Generator by installing it outside of the Program Files folder. Unlike with IL2-MAT Manager, UQMG worked for me even though 1946 was (at that time) still in the default location in the Program Files folder. This threw me off the the trail for finding a solution to getting IL2-MAT Manager to operate, and I wasted a lot of time installing and reinstalling IL2-MAT Manager components.
Lesson learned: if using Windows VISTA, don't install anything IL-2 related into the Program Files folder. I've updated the opening post with this advice.