GM AW is an acronym for Gas Metal Arc Welding, so I'm a little confused as to your question, but my guess is that you're asking ; "I used stick for my root pass, can I now use mig"? The answer to that question would be yes. You need to make sure to clear away the slag left over from the root pass otherwise you will have inclusions. That can be easily done with either a wire wheel, or a wire brush and chipping hammer. After you clean the root pass you can weld over it. Really there is no process that can't be done over another as long as the filler metal is the same. You could mig over tig, you could tig over stick, you could stick over gas, you could tig over dual-shield or flux core, etc... They are all different methods of doing the same thing. The only limitations would be if it were a certified weld, and then it would only be limited because of what it was engineered as.