Adding the ability to change professions sounds like a bad idea to me. I can't see how it would not screw up character balance. All I see are uber characters with Maxed out power weapons and Red pets at level 200. Play a Soldier or Enforcer until you can use a QL 200 weapon, then go MP, Engineer, or Crat and get the QL 200 pets.
I am assuming once someone changes profession, their skill costs would change to that of the new profession, and they would not be able to use the nanos of the previous profession once they have made the change, unless the new profession is Agent of course (I have a feeling most will switch to Agent at level 200 once all our desired skills are purchased at lowest price possible. We will be Full Auto, Burst, Flinging Agents with pets or Brawling, Dimach, Hammer Agents with Pets)
One safeguard of course would be to not allow IP to carry over to the new profession. Meaning you either spend all your IP before you change or you lose it. But when most professions are wielding their highest QL weapons and using their Highest QL pets by level 115, this does very little. Play a soldier or enforcer to level 115 and once you can use that QL 200 weapon, switch to another profession.
Now my final point. Is this even necessary? This is a game where it's possible to get to level 150 in two weeks of twinking (it has been done) Anyone can get to 60 in a week of casual play by grouping. Part of the life of a MMORPG is rerolling. It's the only thing to keep you playing when you've already seen everything there is to see in the game.