This would be much harder today. The TV stations still using microwave are also using digital modulation with encryption. In many ways, it would be far easier to break into a site, and patch in your ASI stream into the transmitters program mux, nevermind that the PID's and other stream information have to be identical or viewers would lose the signal.
I worked in TV during the digital transition and have some idea of how its done. To do it right now would reguire really deep pockets. It would have been a lot easier 20 years ago when the majority of the microwave shots were analog microwave. Back then, all you needed was enough power to overcome the capture effect of the FM demodulator and you were in.
Poet; like in the movie 'Used Cars'

+-RH