TL;DR
Add an entity that can broadcast or receive circuit network signals in a specific channel, such that the channel itself can be set using the circuit network.What?
I suggest an entity or pair of entities that can broadcast or receive signals without wires, including between surfaces, in the following way. The entity connects to the circuit network and has a setting called "Set Channel" which defaults to the abstract signal "C" (for example). Each value of this signal corresponds to a different channel which can carry signals independently of other channels. Each transmitter or receiver entity can only access one channel at a time, but it can switch at any time by changing the value of the "Set Channel" signal. In the case of transmitters, every signal except the specified "Set Channel" signal is broadcast to the selected channel (the exception is to avoid constantly changing the channel of other devices using the same "Set Channel" signal), and signals from multiple transmitters are added, just like placing signals from multiple sources onto the same circuit wire works. Receiver entities read the signals on whatever channel they are set to and can transfer them to the ordinary circuit network. For simplicity I suggest either two entities or two modes: transmit and receive, only one of which can be active at a time.Why?
I recently made a suggestion viewtopic.php?f=6&t=121782 about a possibility for more flexible and precise Space Age rocket logistics using the circuit network, and this suggestion combined with that one would allow fully dynamic automation of rocket launches (and many other things as well) to whatever extent the player is able and willing to set up, without simply doing the work for them. It removes the manual step of the player needing to change the launch ID signal to target another platform. There are several related suggestions for example this one viewtopic.php?f=6&t=121016 and this one viewtopic.php?f=6&t=121440. And of course there is Earendel's AAI Signal Transmission mod, which does something similar.As it stands, all of those ideas are "static" in some sense, which prevents full automation and limits flexibility. Using AAI Signal Transmission as an example (because it is actually implemented), I can have multi-channel wireless communication, but if I want to switch channels I have to open the device's GUI and do it manually. By allowing the channel to be changed using the circuit network itself, we don't need any specialized GUI, we don't need to have the foresight to have named everything correctly in advance, and we don't need duplicate infrastructure for every channel.
Adding a new entity also avoids changing radar behavior (again), and it can be gated using tech or resources separately from radars, combinators, or logistic groups. I think it also adheres to the common Factorio pattern of "one item for one thing, and the player connects them together".