Replacing Runic with Shock

Before I set up my new computer in August and reeeeally get into hacking, I wanted to start with something simple. When visiting Leo's Tomb in WoR with Celes, I'd like her to be able to obtain his sword and replace her Runic ability with Shock. Is this able to be done through a weapon, or would I need to modify a relic? ...or is this possible at all? (The question I ask the most on this site!).