Just to add...because xattr it's also "easy" (for some definition of easy ;)) to add/modify tags from the shell making mass-tagging feasible (as requested by OP). Second answer here should give a decent starting point....
Cautionary
Just to add...because xattr it's also "easy" (for some definition of easy ;)) to add/modify tags from the shell making mass-tagging feasible (as requested by OP). Second answer here should give a decent starting point....