Can I replace the run flat tires on my 2012 BMW 535i with regular all season tires ?

Of course.

yes you can run what you like on your vehicle as long as theyre the right size....runflats are special tires that allow you to keep it moving in the event of a flat

^^thanks captain obvious. J/K. You likely have them because your car isn't equipped with a spare tire like my M5 so keep that in mind. You can carry a compact spare in your trunk on longer trips just in case. If you are running staggered wheels, you can alternatively carry a front wheel/tire in the trunk since it could be used on the front and rear in a pinch. You sometimes cannot run a rear wheel on the front unless you have a spacer to allow clearance of the struts/fender liner, lip, etc. Just make sure you do not buy a directional treaded tire for the spare to allow you to run on any corner.