> You'd also be trolling the air traffic control system

The safe way of avoiding that is to inject it directly into the FR24 feed, rather than broadcasting it as ADS-B.

A considerable proportion of their data is receiving from end-users running their own receivers, rather than the FR24-branded receiver. They do reject spurious data from one receiver but genuine-looking data would be hard to detect and discard.

It's certainly real, the flight path is being tracked in real time by thousands of receivers. You'd need to fly around your transponder to make that, at which point it's not illegal any longer. But if you started DDoS'ing a single point in airspace you're going to go to jail very quickly.