I've done several flybys, both for NASCAR races and more impromptu "panel checks" for the guys on the ground or at the boat. The key is not to be an idiot. Have some SA on where you are.
FWIW....I talked directly to the head of the Richmond office of the FAA prior to doing one of the flybys, and speed was the least of his concerns. Altitude was his biggest concern by far. His exact quote to me was "I don't care how fast you go, but whatever you do, be above 1000' AGL".
That sparked a 15 minute discussion between us about the "250 knot rule". I had it hammered into my head in flight school that the speed limit was 250 below 10,000'. IP's would competely lose their minds if you were 10 knots fast on an approach thinking that they would get violated.
The truth is that while there IS a 250 knot speed restriction below 10,000', if your TMS manual stipulates a higher speed, then you can use that. Further, if you're talking to ATC and request higher speed, most likely they'll give it to you on the spot. The FAA cares a lot more about altitude than speed. They're not going to go through the asspain of trying to get you violated for being at a tactical airspeed (350-500ish?) in the break or during a flyby. If you bust an altitude, you'll probably hear about it.
Does this mean that you can come into the break at 5 bills at LAX? Probably not. SA and good judegement should preclude that.
Having said all of that, if the MILITARY gives you an order not to do something, getting a flight violation is the least of your concerns. This is the day and age where every yahoo has a video camera on them at all times. What they shoot WILL be on the interwebs within the hour. Compounding the problem, and against popular belief, field and general grade officers can and do peruse these interwebs regularly. They will see said video either that day, or the next at the latest.
Follow these rules:
1) Don't be an idiot.
2) Have some SA
3) If you get busted violating the above rules, be a man and tell the truth. Lying will only make things worse.