Someone better will have to answer this to be sure.
However, from what I read you legacy name will stay even if you delete that character. As of now there is no way to change it from your account. That ability is coming "soon" according to the BioWare forum.
I'm thinking my smuggler, trooper, agent and bh will be the only ones showing off the Legacy Name. Shotfir'st just doesn't sound right for a Jedi or Sith.