Four separate units at four different schools. Cummins says they can derate them by limiting fuel flow and putting in a governor of some kind. Their concern is that John Walker said that he AQMD will look at the model # and rating on the tag and won't consider a de-rate. Legally, I don't think they can do that. If its under 50 BHP, it's exempt from permitting and the p-traps per their rule 219. I have a call in to permitting at the SCAQMD.

Good. I think that is the best solution.
You should have all the paperwork you need to prove that a machine has been derated. If it were us doing the work, we would probably retag the machine as well.