I assume you're asking with the 300 BLK in mind? With extreme modifications to a 5.56 or 7.62 you can get them to cycle, but not reliably (IMO). An adj gas block alone will not be anywhere close to sufficient on those calibers. You'd need major mods to the gas port itself, the buffer and spring, and the carrier. Even then you're extremely limited on what loads will work and I've never heard positive things about reliability after it's all said and done. Right to Bear Ammo sells a dedicated subsonic 5.56 upper but it will only cycle one of their loads which is on the very edge of the sub/supersonic line.
With 300 BLK - especially a pistol length gas set up, but also with many carbine length gas rigs - you shouldn't need any modification to reliably cycle subs or supers whether suppressed or not.