In general, whenever a politician tries to reinvent himself into something he's not, it ends in disaster. You should just be yourself and sink or swim with it. Very few end up succeeding by transforming themselves into a different person or character.
Trump was the exception. He went from his longtime "arrogant, ruthless-but-successful businessman" character to hero of the working class. But that's because Trump is incredibly talented at reading the people as a whole and saying what they want to hear. Most politicians can't do that and come off sincere like he can.
Romney should have just stuck to the "solid but practical conservative" routine he had going during the 2012 election, and hoped that eventually the party would move past Trump once he was out of office. The marching for black lives is so disingenuous.