my classification im guessing you mean worker, tauren, giant, ancient, tree, undead, walkable, etc.
to do this (for non ehro units) i'd day create copys of your unit with a different clasification, and use triggers to swich them, for heros.... probably same thing but it would take alot more trigger work
k just checking, in the object editor you can tick "veiw as raw data" so if there something in jass that you can edit a propertie (editing the funny work for unit clasification) then it might be possible, but it might crash wc3