Yes. Let's do specifics using CNJ, ACN, and WHM.

You level CNJ to 30 picking up ~15 bonus attribute points. Those probably go mostly into Mind and maybe Piety.
Now you swap to ACN. ACN starts at level 1 and your stats reset to the lvl 1 ACN stats (modified for race). You level ACN up to 15 earning a few bonus points and putting them wherever.
Now you swap back to CNJ. Your stats and everything are just as they were before but now you can pick up the WHM quest.
You do the WHM quest and get the soulstone. You are now a level 30 WHM with the same stat allocation as you have for CNJ.
You run around as WHM and get up to level 37. Then you unequip the soulstone. Now you are a level 37 CNJ.
You run around as CNJ for a bit more and get up to level 42. Then you reequip the soulstone. You are now a level 42 WHM.
You swap back to ACN and power grind it to level 50! You then reequip your CNJ weapon and WHM soulstone. You are still a level 42 WHM.