Tags are like the Dark Arts. Constant vigilance is needed.
Fix, avoid recreating. That is an insane amount of work.
I just browse
Manage Tags and adjust there (sometimes I do need to search for members).
I clean the Nonsense (to me).
Fiction (that is assumed. I do tag non-Fiction)
Series name (as a tag)
'Identifiers' listed in Tags
'A novel'
I merge name variants. expand abbreviations like SF (I leave things like FBI)
I break apart: Action & Adventure or Mystery and Detective (2 tags)
I also standardize on
and or
&
I use hierarchical with the base the primary. I remove the reverse. It is not needed because Calibre search will find all And I fix those that had periods and got misapplied
Science Fiction.Military
Military.Science Fiction
non-Fiction.Military