I think this is a very interesting question and I would like to know answers from experts. Basically once you get GC, can you go back to a nonimmigrant status, and then come back to GC once again?
When you go to the ttsvisas webpage for a web appointment and try to apply for a H1B at Chennai, one of the questions it asks is "Do you wish to surrender your Green Card and apply for a Non-Immigrant visa?" This perhaps means that you could go back to H1 status.