IBT and whole house transfer switch
Leave the ground rods. Install a second set at the new service location.    

The IBT only needs to go to ground rods.  It doesn't need to go to particular ones.   

This plan depends on there being a ground wire between the old and new rods; it's a rare time when metal conduit shell, water pipe, etc. won't do.

There is no penalty for more ground rods than the house requires.