move the goal line
To alter the rules or parameters of a situation in such a way as to suit one's needs or objectives, making it more difficult for someone else to succeed, keep pace, or achieve an opposing objective. (A variant of the more common "move the goalposts.") Primarily heard in UK. I hate arguing with that type of person. As soon as you start wearing down their logic, they just move the goal line on the whole thing! We're never going to get the book design finished in time if the publisher keeps moving the goal line every couple of months like this!