So as many of you already know, there's this terrific combi bracelet that CASIO made, which comes as an option with certain models. Usually there's a "BC" suffix to the model name for "bracelet, composite" or "bracelet, combi". It makes the GW-5000 pretty much the ideal classic square G-Shock. And it is also capable of dressing up many other square watches, in addition to the 6900 series (all with the same combi-bracelet part). CASIO has also made the combi bracelet for a couple of other models. I know there's the AWG-M100BC, which is a smallish digital-analog watch. It was also used in an Aviator and I think a ProTrek. It's not exactly the same bracelet for all of these -- the end links are shaped differently, so you have to order a different band.
I've got a GW-M5600BC that I've had for a good many years and bought a 2nd bracelet for installing on a GW-5000... but as things turned out, I've still not landed a GW-5000 yet (I've been aiming for a used one having scratch free glass and DLC for around $150~170 USD--which I've seen come up before and missed). But while servicing an MRG-1 that I've got, the idea popped in my head to try test fitting it. The lugs are compatible. But, the bezel is not 100%. More like 90%. Still, it's not bad and looks perfectly fine from a distance.
As you can see, there is that slight corner jutting out on each side. If I decided to make this combi-bracelet dedicated to the MRG-1, I'd take a sharp knife and shave them down to mate well to the bezel (but then they may not look proper on a GW-5000).