The numbers may go down but they may not stay down or they may not go down. It is said that it is pointless to keep BATing a dog with MVD because the results will always come back high.
A change in food should not cause liver enzymes to go up.
Maybe if it was very high in protein (not the case here) but that really isn't agreed upon.
If hemolysis occured, the results could be skewed:
Hemolysis - Wikipedia, the free encyclopedia
If the blood for the panel and the BAT were drawn separately, this probably isn't the case because they are both "off."
Any vet can order tubes for the Protein C Test and perform it.