It seems to me that LEOSA would only cover the firearm and not the magazine.
At the risk of deconstructing to the point of minutiae, if the officer is issued, specifically trained and carries a particular gun with a particular magazine utilizing particular ammunition in the performance of his duties, any alteration to such a configuration would be outside the scope of employment and exclusive of his role as a police officer. Therefore, if the officer's duty configuration includes a P226 with a 12 round magazine filled with JHP's, and that is the way the officer is trained and with which he is required to qualify then it would stand to reason that carrying off duty in that exact configuration is in compliance with HR218. A firearm without a magazine is useless and contrary to the intent of the legislation.
Although a specific amendment addressing hollow point ammo (to address NJ regulations) was added to the law, magazines are not excluded from the definition by statute as are machine guns, destructive devices and the like. Considering the laws in existence regulating magazine capacity in several states, perhaps this should be addressed in a future amendment.