Well, from what i've seen from a bit of experimentation.... the answer no, not possible.. at least not elegantly. However there is various kludges that would sort of do something similar, maybe.
I know that if you can actually get a champion to end up with 2 paths... they can choose traits from either path. It doesn't look great though, the 2nd path is hidden and you have to scroll with the mouse wheel to see it. It functions fine though.
I tried to have a trait that you could select (on the General tab) that would give you a 2nd path (path just granting you the Path ability). It didn't seem to work. I might try it again at some point but it didn't look like it worked from my first effort.
I reckon what would work though... is you could have a trait available, say on the General tab... called "Warrior Training". It would unlock a spell called "Path of the Warrior" or something that could only be cast if you had that spell... and you can only cast it on yourself. When you cast the spell it would give you the 2nd path (Warrior in this example). You cold have a minimum level restriction (6 in your example) on the "Warrior Training" trait.
I'm fairly sure that would work. But it's obviously a bit fiddly. And it would not prevent you from picking traits in your original path.... to stop that you'd have to somehow get rid of the 1st Path ability which I don't believe is possible (and HF seemed to also indicate it's not possible).
Now, that's from what I discovered in like 0.50. Things may behave differently now. And will likely behave differently in the future, at least up until release.
