No, I don’t recall the entire leadership of the party changing when the nominee for President is firmed up. Normally, the party committee’s job is not to get any one person elected, it’s to organize the fund raising and spending efforts to give the party the best shot at all the major races, from President to Congress to Governors and State Legislators. Since the President is the biggest job on the ticket, you always expect the party leadership to back their nominee, of course. But I don’t recall changes this major this close to the convention.
This is likely an attempt to make sure the RNC pays his legal bills, and doesn’t move to abandon him, even if he gets convicted.