Well I am no expert on E175's but someone mentioned before that there are different versions of E175's with different MATOW. The compass 175's were over the weight allowed which is why they were grandfathered. If there is a version of the 175 that has a weight below that than it can be swapped out. Now the question would be is if the 120 76 seaters has been reached then the 175's that would be swapped will have to be 70 seaters. Maybe someone else with more knowledge on the E175's will chime in on the different versions.