Actually, Magnum was allowed to wear the "Budweiser" with his Navy dress uniform. See the top photo. That big, eagle shaped badge on his chest is the SEAL Trident Qualification badge. The show made it very clear that Magnum had been an intelligence officer in the Navy. They never explained why Magnum was awarded the "Budweiser," but it was implied that he operated extensively in the field so it isn't a great stretch to believe he either received UDT/SEAL training, or was somehow grandfathered into the badge when it was commissioned by the Navy in the late Seventies.
I know, I know... you think it was probably a wardrobe department mistake and I'm making too much of it. Rubbish. This was a Donald Belisario show -- the guy who gave us JAG and NCIS -- and Belisario was a Navy vet. He wouldn't allow a mistake like that. No way. No how. Navy sailors all know what it takes to earn the SEAL Trident Qualification badge. And Magnum was wearing it on the show long before the SEALs hit the pop culture lottery and everyone and their mother had heard of them. But SEAL training or not, Magnum was never a superman. He was beaten up, ambushed, disarmed, out-fought, and physically embarrassed at least as often as he wasn't. But Magnum did show the one universal trait of SEALs, real or fictional: he never, ever, gave up.
And in a new movie, would we get a classic Ferrari, or an update?