It is impossible to easily change the Bitcoin protocol. Any Bitcoin client that does not conform to the protocol cannot force other users to follow its own rules. With the current protocol, double spending on the same blockchain or spending without a valid signature is impossible. Therefore, it is impossible to create a large number of Bitcoins out of thin air, use other users' funds, destroy the entire network, and the like.
However, the majority of miners may arbitrarily choose to freeze or reverse recent transactions, and the majority of users may also exert pressure for some changes to the protocol. Because Bitcoin can only function properly when all users reach a complete consensus, it is very difficult to change the protocol, requiring an overwhelming majority of users to adopt these changes so that the remaining users have no choice but to follow. In general, it is difficult to imagine why a Bitcoin user would choose to adopt any protocol changes that may endanger his funds.
