It's possible..just read guides on forum nothing is gliched i guess
All you have to do is finish your culti and after that you will be able to change. I have done it with all my toon's and never encountered any problem.
An Hour or 2 depending on how fast you can find a PT to do the full GV run.
I had a lv150 sage Barb. but I realized it is not as powerful as Demon Barb.