I had this problem. Yes, you can unscrew the top and bottom plastic bits but that doesn't fully release the ally panel. They're stuck on with, if I remember rightly, sticky pads. Removing it won't be easy. I gave up becuse I had a spare lid. Even changing the lid is tricky cos you have to drive out the pins in the hinges. I managed this with the aid of a nail used as a makeshift drift, but it's fiddly.
Also, be warned that if you order a lid, believe it or not it does NOT come with the R1200GS decal, that has to be bought separately. Or, certainly, that was the case in 2007 when I needed one. Suggest, perhaps, use of Two Wheeled Humvee's excellent stickers.
Good luck.
Geoff