Just like any other network rules, the block reward could be modified through hard forks. If you convince everyone to run your client with the new block rewards, then you have effectively increased the supply limit. Anyone can do this, not limited to the creator. The whole point of Bitcoin is for anyone to be able to make changes and people can choose to or not to follow you.

Anyways, there is no economic incentives to do so. It would just devalue Bitcoin.