If the majority of people decided they didnt like the current rules (eg all the people complaining about bitcoin deflation) they could very well change them by simple agreement.
One can't simply force a change to the rules. All you can do is make a hard fork in the network. If nobody adopts your hard fork well you can keep mining worthless coins but people can continue to use/mine the existing fork.
Bitcoin is highly resistant to change (almost to a fault). It is a common myth that the person who controls the majority of hashing power can change the rules.
Of course, this is only possible becuase your chain looks as if it was following the rules. If you have a non malicious computational majority, than any change in the rules would make an incompatible block-chain and a hardfork.