If you have done a voluntary change of you booking, then the seat reservation is not reimbursable. That's LH rule.
Concerning *G not counting anything on LH, I only can state that this is reciprocal at UA for LH *G. I am HON ( equivalent to UA GS) and don't get any better seat with UA, will say when I fly Y with UA, my seat is always in the "cheapest" section. Never get moved to Y+ or something like this.