Without knowing the exact certification standards, I'm going to make a wild guess here and say that the R22 would have some trouble passing certification if it were to be developed today.
The autorotation characteristics and the lack of reserves when it comes to engine-off landings are bad enough at 1370lbs, and whoever had to establish and verify that H/V diagram must have had balls of considerable size. Increasing the weight would make it worse. No way that would be allowed, unless a bunch of other parts are changed as well, and as others have said - once you start going down that road, you'll soon have to change the whole helicopter.
Out of all the machines I have flown, I would say the R22 is the LEAST suitable for a MGW increase. I have around 2,000hrs on type btw.