The movies shouldn’t be an issue regarding nfo files normally as they probably were, and will continue to be scraped from TMDB. Individual episodes of TV shows also shouldn’t be an issue with local files as the only urls they have normally are to art that most would have sitting locally and therefore never get used. The issue I was referring to in the other thread is just any tvshow.nfo files you have in the root of your individual shows. These are important as if they contain a link to source the info from TVDB and you set your scraper to TMDB then any episodes that don’t have their own local info will not get added due to not having a valid online link to the shows scraping source.
If you have a show that is already canceled and you have local info for all episodes then it is fine to use the old tvshow.nfo file. I would recommend deleting the <episodeguide> tag as that has caused some issues in the past (ie purposely removing the online link since you are not going to need it). I have a few show I keep like this due to not wanting it how TMDB has some titles (like wanting SG1 movies as specials in the show instead of separated in the movie library).
The way I personally would do it is on a PC connect Kodi to a new db name and setup everything there. I think it is a bit more convenient and quicker to mess around with a mouse and a keyboard than a remote with this mass library editing kind of thing. Once your happy with how things work on the new db on your PC then you just go to the clients and change the db name in advancedsettings.xml, delete the artwork cache, and start Kodi back up. About the only complication I see for you is that you are using local mounts. because of this you would need to (unless your PC is actually Linux with the same mounts) need to add a path sub to Kodi so the db stores as mnt/media... even though you would probably be accessing this share via (I’m assuming) //nasname/something.