I'd like to program a transmitter to output a routine each time a button is pressed. That way I don't have to be connected to a computer each time I want to use it. Does something like this exist?
Sure, there are embedded devices like the Ettus E-Series you can set up to do this. Note you'll need some experience in embedded systems if you want to use such a system. However, for low-performance apps (e.g. low-bandwidth signals) you might be able to simply run a GRC flow graph on your embedded device without a lot of modifications.