This is one of the new features of Version 2019.0 that you might have missed. The replace crew feature has been around for a long time allowing the estimator to swap out one crew for another. But the issue was it would also replace modified crews which for me could be an issue. I would have to find the modified crew activities and uncheck the box. Now there is a box to hide modified crews so that only the crew as it exists in the crew setup is shown. It really makes this feature much more useful. Check it out.