A change to Bitcoin's total supply would require a hard fork; which obviously, a lot of people are against(both with hard forks and increasing of supply). So you might as well say it's next to impossible.
I think this supply isn't enough for world-wide using and mass adoption, so is Bitcoin supply really finite and unchangeable?
How is it not enough? Bitcoin is highly highly divisible. If you can't buy one whole bar of gold, then you buy a gram of it. Same thing with bitcoin. As bitcoin's price goes higher and as bitcoin gets widely used for merchant payments, probably expect us to be using the "satoshi" or "sats" denomination sometime in the future.
1 Satoshi = 0.00000001 ฿
10 Satoshi = 0.00000010 ฿
100 Satoshi = 0.00000100 ฿ = 1 Bit / μBTC (you-bit)
1,000 Satoshi = 0.00001000 ฿
10,000 Satoshi = 0.00010000 ฿
100,000 Satoshi = 0.00100000 ฿ = 1 mBTC (em-bit)
1,000,000 Satoshi = 0.01000000 ฿ = 1 cBTC (bitcent)
10,000,000 Satoshi = 0.10000000 ฿
100,000,000 Satoshi = 1.00000000 ฿
Source:
https://www.btcsatoshi.com/