adafruit rf m4 as a ground switcher
From the description of the microswitch function as provided, it seems the "microswitch" is a momentary pushbutton (as opposed to a toggle / DIP switch) connected between a pull-up resistor and the lighting controller's ground. If so, the solution for replacing the push-button functionality using the remote is simple. 

From the AdaFruit product description:


  The M4 momentary type acts like a push button - when the A button is held down, the matching pin goes high. When the A button is released, the matching pin goes low. The pins only go high when a button is pressed


In order to use this momentary positive pulse to achieve the equivalent of the pushbutton momentarily shorting a pulled-up line to ground, a N-channel MOSFET can be used, thus:







simulate this circuit &ndash; Schematic created using CircuitLab

Explanation: 


When D2 goes high due to a button push on the remote, this causes the gate of the MOSFET to be driven high.
The MOSFET thus conducts, acting as nearly a short circuit (a fraction of an ohm), similar to what the "microswitch" push-button does.
When the button on the remote is released, D2 goes low, and the MOSFET stops conducting
This schematic will allow either the pushbutton or the remote to switch the lights, as they are hooked up in parallel.