reorganizing tags

my tags list has grown someone organically as i need them but now i'd like to organize them into groups of related things. like a group for material type: wood, stone, metal, etc and another group for weapon type: bow, gun, knife and another for ammo type: bullet, arrow, etc you get the picture

there doesn't seem to be a way other than deleting everything and starting over
am i correct or is there a better way?