I’ve flown into Philadelphia many times. The Wells Fargo Center (where the convention will be held) is only a few miles from the airport (both are situated along I-95), and directly in the flight path for planes coming into Philly International. I guess the approach will have to be rerouted over south Jersey.
Schedules airline flights to/from an airport are under ATC control. No problem. No issue.
The NOTAM is to restrict media and joy-riding minions clogging the airspace and causing an unsafe operating environment.