OK, I just bought a new R1150GS, and I intend to lower the muffler to allow use of a full size left bag. The police GS list shows three parts:
99 99 0 000 489 BM BMH Muffler Mounting Bracket $98.79
99 99 0 000 491 BM BMh Muffler Adapter Pipe $42.79
99 99 0 000 490 BM BMH Muffler Heat Shield $289.79

As I read this, I see the 491 adapter pipe as the actual part that allows repositioning of the muffler. The mounting bracket attaches to the original support bolt but with a longer length to drop the muffler to the new angle. The heat shield 490 apparently is a new cover for the muffler, with a repositioned shield over the pipe elbow area.

I have part 491 on order, and intend to construct whatever support bracket is required. I think the $289 for a new heat shield is a bit pricey, just to get the little cover at the bottom end. I think it should be possible to either cut off the small cover, or trim it to fit the new location. I've seen aftermarket pipes that don't have a cover over the connector pipe, and don't look out of place.

So, anyone done this on a GS? Any advice to offer before I take things apart?