No one is talking about FTL transmision of agitprop which wouldn't work regardless of the price because the local population doesn't have anything to recieve that. We're talking about Comstar using their position to transmit radio or TV to the local population.
You assume that would be allowed both by the memorandum of understanding that allow ComStar to operate in the DC and CC (and the other states), that one or more rulers wouldn't use this as an excuse to move against ComStar for interfering in their domestic affairs (which in arguably IS from that POV), and that ComStar wouldn't like the deniable consequences when the moves are made. Also all five states have had rulers who were unstable and looking to pick a fight with folks (Jinjiro Kurita, Claudius Steiner....)
("Oh dear, Precentor Sian's jumpship was boarded by pirates who tortured everyone on board to death horribly as he returned from Terra? Tsk, tsk, tsk, we wish we could help but the CCAF is
so overstretched these days with the two front war that we're in heating up. Why, CNN was doing all that reporting on our military reverses in fact, as you know. So we'll do what we can, but those pirates are halfway to Tortuga or Antallos by now I suspect, Primus. Pity he can't support your budget proposal to expand CNN's coverage next month, isn't it?")
A large part of ComStar's power rests on that neutrality, but it has limits. Overtly meddling with the internal stability of the DC and CC is a big red line to cross (and also remember that ComStar didn't spring into existence with ROM fully formed and until 3050 they have jack shit for military deterrence should a House Lord send a Mech Regiment to carry that Cease & Desist letter to Hilton Head).
If push comes to shove, there's ways to preempt an Interdict by storming the HPGs
first to screw guns into the ears of the staff (Amaris did it with an 'everyone move on date X' Christmas message to his troops with a codeword that told them to go on sealed orders). If I were a sneaky House Lord, I'd even have the ISF or MASK 'distract' Comstar by a WMD attack on a major HPG station... in a neighboring state or states... before I made my move. Have DEST or the Death Commandos drive a nuclear weapon in the back of a delivery van into the say Kathil HPG station for a little deniable suicide bombing to get the Davions Interdicted to take them out of play for your own Interdict....
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Also, you're missing the point of the hardware being sold int he DC and CC.
In order to not hash each other's signals, TVs and radios are broadcasting on specific frequencies.
NK consumer electronics are physically incapable of picking up unapproved TV and radio broadcasts until rewired. So Comstar News Network can broadcast on 30 Mhz as their assigned station, but the Dragon's Ear Home Entertainment Centers skip from 20 Mhz to 40 Mhz when you change the channel. And if you try to cut in...well too bad so sad, this new pirate radio station two blocks away from your transmission tower is broadcasting on a frequency that interferes with yours and is turning your signals to hash.... (which is how E-WAR fundamentally works).