Sorry for the delay - major email upheaval needed sorting out.
My one suggestion would be to not add the tunes to iTunes at all, but open with something like VLC instead. Double clicking will add them to iTunes, and if you do this by mistake remove from iTunes as soon as you see the mistake. I do this with a few collections where the tags are so messed up I have no energy to alter them.
I share only some of my iTunes library folders by name. If I wish to share some and not others by the same artist I rename those I don't want to share Artist-A and do not share those folders. Not maybe ideal for you, but worth a thought. Also if you want the files in iTunes, add them to the library but first change the setting in iTunes preferences : advanced to not add to the iTunes music folder, but remember to change it back afterwards!