The only thing you can grandfather in is pay and bidding seniority and only at the top level. Once you start hiring pilots into more senior positions at higher pay it won't matter anymore because those senior pilots who have already been there a long time will be competitive in their own right.

They may resent the changes for personal reasons that have nothing to do with pay but that's their problem...they'll get over it.

Change is always disruptive and can never please everyone. It's about creating change that benefits the whole and allows regionals to survive and for pilots to earn more money at lower costs to the airlines.