thanks all, especially the concrete answers some of you threw out.
Let me help answer my own question, but don't let that stop the conversation keep going.
I just called the HPD firearms phone number and a civilian sounding lady (odd, as I've only ever seen uniform males working the windows - all two times I've been there - maybe she was a clerk in the back?) told me no problem. She said something about a new $42 fee since DEC 2016 (dagnabbit! I got my PtA n Oct or Nov!!!), but otherwise okay.
Of course all of this discussion is about long arms only. Also, on the Louisiana side of the equation, they said must be LA resident for pistolas but no problem for a long arm. This was all just three-minute counter talk so I'm not positive, I've not yet tried to actually buy one here. Yet...
FYI, I was thinking that opportunity/price would be a very compelling reason to buy one while here vs buying one in Hawaii. But I just cold-called a couple/three of the more well known gun shops back on Oahu and many guns similar to what I'm looking for are available in Oahu stores and also close to or right at MSRP. So price/availability does not seem to be a really big 'plus' to buying on the mainland. If anything, a 'minus' might be the hassle of buying a case and paying airline to check it as baggage.
I still may buy one up here, just because I KNOW I can get one here because I see it on the rack right now and if I get home it'll turn into an "oh, we just sold the last one last week" or "we don't carry that model anymore but can order it" story...
Also, any chance I get to do something non-traditional with Hawaii's "isms", I do it. I buy all my vehicles in Washington and ship them in Matson. And STILL save thousands. I respect the free market - if a Hawaii merchant wants to treat me like a captured audience, then fair enough. The flip side is if I can get something on the outside and bring it in, then fair enough right back at em.
But definitely don't let this stop the conversation, keep going with the anecdotes they all help to inform us..