If your dealer is refusing to perform the recall without you paying to have mods removed, I implore you to open an NHTSA investigation at the following link:
https://www-odi.nhtsa.dot.gov/VehicleComplaint/
This is explicitly against the agreement that Subaru entered into with the NHTSA and puts them out of compliance. Dealerships are going to keep doing this until they're held accountable to the law. File these reports and let the dealership know you are doing it. They are subject to a fine of up to $21,780 for each vehicle they refuse.