Anyone who changes that supply limit number won't be changing Bitcoin but they will be making a fork and it will be some shitcoin. Bitcoin will not change the 21,000,000 supply. Shit man, blocksize brings enough of wars, imagine someone trying to change supply.
Didn't some forks like Bitcoin Diamond already do that? They're shitcoins (most are even scams), but they do exist. In fact, I believe one of the main reasons Bitcoin Diamond has been forked off the Bitcoin chain was because they considered it's harder for newcomers to accumulate an entire Bitcoin, hence the 10x increase in the supply.
Well they didn't need to change the supply, truth is those shitcoins are always worth nothing anyways, at 21,000,000 I'm not sure they'd be worth a buck a coin when it's just a shit fork.