It's quite possible to produce new TV and Radio stations in PZ by using the WordZed tool. I'm not sure how easy it would be to add to existing radio stations given that (apparently) if you use the same TV/radio "frequency" it removes the ingame stations and replaces them with your own.
I've managed to create at least two radio stations for a Mod I am working on, I'd post a screenshot or two, but I'm not at home so I can't access the Mod/game to show you, but it is possible. There have been another two mods previously which were published, but seem to have since been removed.
Anyhow, that aside - if you download WordZed, you can look at the ingame "RadioData.xml" file and possibly modify that. Alternately you can add new TV/Radio stations separately. To do this you'd need to create your stations, export them from WordZed, upload them to Steam as a Mod and download it that way (I think that is the only way, you may be able to drop them somewhere in the games files) then activate the Mod via the ingame Mod GUI.
If you are still interested, I'd suggest looking here for the tutorial and the tool: https://theindiestone.com/forums/index.php?/topic/21318-wordzed/
You can also download this Mod which can act as an example: https://steamcommunity.com/sharedfiles/filedetails/?id=975088107
(Edit: Feel free to ask me some questions, but I may take a while to respond as I'm not on the forum that frequently.)