I would think you could have this done. I had the opposite done. I had the MGB that was revised to a gastric sleeve because I lost too much weight. Seems to me they would just need to go in and bypass the intestines like they do in the original MGB, since you already have the stomach part done.
~Kim~ , 202-start/125-goal/124-current
MGB 11/15/06, Revision to Gastric Sleeve 11/30/07