I'm a former resident of Essex county, when there owned a business, had employees, was a Republican committeeman for a number of years.  Own property there on land owned by family for over a hundred years.  Learned to shoot there.  Learned to hunt and fish there.  My grandparents and parents are buried in the town cemetery.  But I am a nonresident that now spends summers and falls there.  All my gun owning neighbors have fancy ARs and knowing them most all my life, I'll bet they have not yet gotten around to registering theirs.

I won't bring handguns into the state any more.  I used to.  The risk is too great now.  I was a permit holder as a resident, but it's not valid now.  I want to have and shoot an AR type 5.56 I can carry in and use, then carry back home to my free state of Florida.  What risk do I have doing this with a fixed mag 10 round Smith M&P Sport II AR 15?

Fixed mag? No risk at all. It's not an evil "assault weapon" in NY.

You still own property there you can still retain your permit.
As for your neighbors who "haven't gotten around to registering their ARs", their window of opportunity to do that closed years ago.
If your fixed mag rifle is NY compliant you can have it. I'd rather switch to a plain Jane rifle like a mini than try to deal with a fixed mag rifle. Of course they're going after all semi's eventually. Just a matter of time

Order a Bullet Button (readily available for under $20.) Installing it takes all of three minutes with the included tool, buy a ten round Mag-Pul magazine and enjoy yourself.
Usually those that "get in trouble" do so because they were doing things to get them in trouble, and the farther you're away from the Flag Pole the less you're likely to be noticed. There seems to be a hidden talent among New Yorkers above the I-90 of remaining discrete in their possession and use of Guns, and it's always sound advise to follow that advise.

I don't think that AR's with bullet button are legal in NYS.  The mag has to be "permanently attached"

I don't think the word "permanent" is in the safe act anywhere. Because nothing is permanent anyway.

I believe it says it needs a tool to remove the magazine. If it removes without a tool, it's no good.

Right?

The Bullet Button is neither "Legal" or "illegal"  arguably, once a magazine is locked into place with one (and ostensibly sealed over) then the magazine is no longer Detachable...it can be removed with a Tool, but removable and detachable are not synonymous.
"You can remove the engine from your Car, but you can't detach it."

If you run the internal nut all the way down there isn't sufficient travel to release the magazine.
If you drilled & tapped the magazine button to something like a #4 or #6 machine screw and threaded it in until bottoming out, the magazine can't be removed.
It's NY and you never know who or what, if anything or anyone is going to give you crap about the evil rifle, and even if they do how far is it going to go?