It's certainly possible to do this, but I'm not sure its a good idea. Doing it would be making calibre insist that any element which is aligned center have no text indent. That is not always correct. text-indent applies to only the first line of an element. So someone could, for some reason want to affect the indentation of the first line in a centered block. I cant think of a reason why they would want to do this, but experience has taught me that someone, somewhere will
It should be relatively simple to create a plugin (or add an option to the modify epub plugin) to do this to an existing epub witha couple of clicks.