I read a thread on this some time ago. I don't remember the specifics.
I've never looked into doing this but, IIRC it's technically possible. I am unsure about animations.
I did a brief test with forage for a human warrior.
I changed `skill_caps` table to allow it in the DB and added <pp->skills[SkillForage] = 5;> to <Client::SetClassStartingSkills>. It showed up proper in the DB when creating a new char but, not on client. I use Titanium client.