However there are some things that even the combi programmer doesn't give you access to. I was playing around with, for example, a way to modulate a ReDrum pattern rate via CV, but there is no option for it in the combi programmer. However, there is an option for remote override mapping. This feature lets us map a parameter to a MIDI controller.
Now what is great about Mac OSX, is that it comes with a fairly easy to setup virtual MIDI driver (the IAC Driver). I've found this to be very useful when I can't find any way to achieve a particular setup in reason through existing devices.
By assigning the rate parameter on ReDrum a remote override, selecting the IAC Driver as your control surface, you now have access to all your standard MIDI expression and CC controls. Assign the parameter to one of these controls.
Now, create an External Midi Instrument device in the rack and set this to your IAC Driver Bus 1. You can now put this in a combinator and use the programmer to send CV to all of the IAC Drivers MIDI controls. Thus allowing you to send CV to any other parameter in the Reason rack that you couldn't ordinarily access via other methods, so long as it also allows for remote overrides.
I've not yet done a deep dive check out how many other things can be done with this method, besides rate modulation on ReDrum, Matrix and modulating the Reason sequencer tempo using CV. Here is a little video demonstrating the effect I was going after, using the method to modulate the rate of ReDrum and Thor via Matrix, with PSQ generating the CV.
It's not incredibly useful if you consider you can create sequencer tracks for a lot of these parameters and then pencil in your automation, but this opens up these parameters for more generative CV modulation as well as makes it viable for live performance.