FM broadcast RDS injection

I'm looking at a elektor electronics Fm transmitter with an atmel processor that generates the 57kc subcarrier for the RDS display, and puts a station name onto it.
The idea is you can have your own mini station with RDS display and be able to use the traffic announcement function.
I'd like the use the display of a radio while its receiving a 'proper' station, ie take over the RDS station name without affecting the stations audio reception.
So this would require filtration of the original subcarrier, then injecting the new one.
I'm reasonably familiar with Rf.
Any ideas welcome.

would this be for retransmission? or just injecting into the radio? you could just take the baseband subcarrier signal and run it into the radio (cut the radio's subcarrier filter off from the detector output and connect your transmitter's subcarrier there. that's assuming you can get at that part of the tuner circuit.... most of the FM tuners these days have one very tiny chip, and very little external support circuitry, and are controlled by an SPI or I2C port. doing it by manipulating the RF with filters might be difficult because it would require almost "brick wall" filtering to strip off the two RDS sidebands. another way to go about it (assuming you have another tuner or receiver) is to feed the transmitter with audio from a separate tuner, add the RDS, then feed the result into your receiver with the display.

Yes I think my original idea is a bit too technically difficult.
My idea is to be able to use the radio display in a vehicle independant of anything else.
I had another idea, less difficult, make a low power tx, tune the radio to it and set it as a traffic announcement station, then when required send it the data to say theres a traffic announcement, switching the radio to the transmitter and displaying its name, or in this case a message.
This cuts the audio but only for the time the message is present.
The only issue with this is older radios just say 'traffic announcement', newer ones say both that and the station name, or one then the other.