Not me, I'm quite happy with it the way it is, except I may want to try a one tooth taller front sprocket in the future.
The C5's come with a 18 tooth sprocket.
I don't think your going to fit one much bigger than that in there.
If you look right behind the sprocket there are 2 bolts going into this boss to hold the outer cover on. An 18 tooth comes pretty close to that boss. If they do end up making a 19 tooth sprocket you might get it in there with some grinding but the chain itself might hit the case on the front side. The case is pretty thin there and I don't know how much grinding it would take.
No matter what sprocket you run it would be wise to keep good chains on the UCE's because a broken chain would wipe the case out for sure.
Now, the 18 tooth C5 sprocket on a G5 is a perfect upgrade. That motor would definitely handle a 19,20 or a 21 if they would fit.
CJ