When you install from the public library in the IDEs do they go to your one “external” directory shared among your projects or do they go to the Extensions directory in an individual project’s materials directory? Or do you have a choice? If they go to a common directory, the following is an important warning. If they can go to the materials directory and that’s what you’ve been doing, it’s not.
Though the IDEs let you use the 10.1 or 9.3/6M62 compilers (or 9.2/6L38 or 9.1/6L02 if you really want), they only support one External directory and the Public Library is pointing only to extensions for 10.1, most of which would not compile with previous versions. So if you have an existing 9.3 project that relies on a given extension you’d installed from the (old) Public Library, and you’re playing around with 10.1 and install the new version of that extension, it’ll clobber the old one and you’ll be unable to compile your 9.3 project again without manually moving some things around.
So if you have existing 9.3 extensions installed in your External directory and existing 9.3 projects, you may want to create another user (who would have its own External directory when using Inform) and let it compile with 10.1 while your original user continues to compile with 9.3.
If your project does rely on third-party extensions (or you’ve written your own extensions with I6 inclusions) switching back and forth between 9.3 and 10.1 in the same project will be a problem. If it’s a straightforward pure I7 project with no third-party extensions (or only third-party extensions that don’t use I6 inclusions) you’ll probably be fine.