Tags are basically space reserved inside the music track file where text can be written that describes the music, such as Artist, Album, song title, year of release, music genre, etc. The Brennan units do not use the tag information, so there's no need for it with Brennan units. Many people want the tagging information so that it can be used by other devices, say in the case of NAS or Sonos. Personally, although I don't currently use the tag information, I make sure it's there just in case I ever need to access my music that way in the future.
As for your current problem, it seems unlikely that just tagging an album would be the cause. It seems more like it was a coincidence with your SD card software being corrupted.
The only way that I know of to remove the tag info is to do it manually via NAS. I believe you have to have a program that can read and write tags to do it. I don't personally know which such programs might be native to any OS. But I know mp3tag can do it, and I think that's a free download.