First, I deactivated the magazine safety. In my opinion, magazine safeties aren't, for both tactical and safety reasons.
On the FiveseveN, a spring bar is pushed up by an extended rib on the right side of the magazine, putting pressure on the trigger bar, and allowing it to contact the sear. The trick is to keep pressure on the bar, even with the magazine gone, to trick the safety into thinking everything is ready to fire.
After reading about various ways of disassembling the weapon and removing the bar, I settled on the "10 second fix", which can enable or disable the magazine safety without taking anything apart. This borrowed image shows the safety after it is disabled:
The bar is usually below that little block, where the magazine rib can bend the end upward, contacting the trigger bar. I used a knife blade to pry the end of the bar away from the side enough to slip a small screwdriver blade underneath it, and then lifted it above the block, where it puts full-time pressure on the trigger bar. To enable the safety, just pry away the end of the bar, and move it into the slot below the little block.
The other tidbit was the arrival of a couple of CMMG +10 magazine extensions for the FiveseveN. When 20 rounds isn't enough, you can have 30.
The plastic FN magazine is built much like the Glock, with a tab in the middle of the bottom edge locking the magazine body to the floorplate. My Glock mag tool came in handy, and with just a little squeeze the floorplate slid off. The extension, with its longer spring, attaches to the mag body like a floorplate. Then the original floorplate in again placed on the bottom.
It's not elegant, but it is 30 rounds in a handgun.