I don't conceive it possible coz I'm a bitcoin admirer as well as its believer, Satoshi is my god and god's intention cannot be changed. provided that someone is here to change the amount of bitcoin, then maybe Satoshi will land and forbid it. Bitcoin is limited and humans won't reach a consensus of enlarging its number. when bitcoin's amount rises, bitcoin is not bitcoin any more

Anyone can change the codes because now everyone can learn about the blockchain and build their own. But it cannot be the original bitcoin that is what the blockchain and decentralization is about so yeah God is unique.
^ Yes, you are right that they can modify the code because that is open source code but no way that they can change it. If that will happen, it will change everything and should accept by everyone. BTC code should not change because it will create a conflict to the network that against by the users and the miners of BTC, if that will change, it will change everything. That is why we have different forked coins to BTC, they created a network that similar to BTC but actually not the same when we talked decentalization.