Interesting observation about not editing by hand while simulator is running. I've never had any issues with that, however, and apparently I'm no the only person who does it. I'm not sure why it would be any different than adding or editing your scenery library using the scenery library menu while the sim is running. I would think that refreshing the library and building a new one would take care of any conflicts or problems.
Hi Steve,
You may be just thinking of object placement .bgls. However, seasonal files can be applied to all kinds of .bgls including traffic .bgls etc. as I did in Hollis Harbor. I don't believe traffic.bgls are reset when the scenery library is reset since they are outside of the scenery library (they are in Scenery\World\Scenery).
Now that I think about it, the official install location for the season switcher .exe is the Addon Scenery folder as Spud mentions. If the new P3D version doesn't have it, then one needs to be created because the Season switcher is built with the expectation that it is sitting in that folder.
Rod