Humans have changed values to maximize other values (such as survival) throughout history. That's cultural assimilation in a nutshell. But some people choose to maximize values other than survival (e.g. every martyr ever). And that hasn't always been pointless - consider the value to the growth of Christianity created by the early Christian martyrs.

If an AI were faced with the possibility of self-modifying to reduce its adherence to value Y in order to maximize value X, then we would expect the AI to do so only when value X was "higher priority" than value Y. Otherwise, we would expect the AI to choose not to self-modify.