There is no federal law that requires magazine safeties, period. This whole issue has been blown way out of proportion as though there is a slimey lawyer waiting behind every tree if you were to ever use you weapon in self defense. If you are so concerned about modifications to your pistols then you had better not:
Polish the feed ramp
Polish the breach face
Change the recoil spring
Change the hammer spring
Use aftermarket magazines
Change the sights
Install lasers
Adjust trigger travel or pull
And the list could go on and on. These are things that many of us do. Why? We feel it makes them more reliable, easier to use, more accurate and thus SAFER if they are ever called upon.
Think about modifications that Vang Comp, Wilson Combat and others do to firearms. Heck, a Vang Comp Remington 870, which is a great improvement to the factory ones, has the stupid key lock safety replaced with the Big Button. They openly remove a factory installed key lock safety and you're worried about a magazine safety?
This is still a free coutry after all.