Each magic is set up differently, and will fall under numerous categories ( not all of them magic ) like you can have spell A fall under "Magic" and spell B fall under Skill, a character who doesn't have the "Skill" command won't be able to use spell B.
Just change the char battle commands, or change the category of the spell.
Unless your talking about abilities like "Fight"?
You have to set the abilities. Just go to class set up, and put in the skills ( magic, fight, earth magic etc ) you want, make sure the stats match of the original char and then give that class to the character you want. That's how I do it. Make a class, not a char.