So the solution is to delete the body data for the h slot, then reinstall the C12DS grendel, then copy the grendel's data to all age groups. This way, when next I inject a tree hugger into the world it won't overwrite the grendel body data.
So for deleting the existing data, to remove slot h I'd remove files like a12h.att and b14h.att correct?
That's correct. I don't have C1toDS installed right now (I've just upgraded my computer for Guild Wars 2 and am in the process of installing everything) but the possible files you will want to look for will be:
(a-n)10h.att
(a-n)12h.att
(a-n)14h.att
(a-n)15h.att
where "a-n" means any letter between a and n