Two separate functions of 5282 RC remote?
With only using existing non-modified LEGO parts a mechanical solution with a servo motor, two polarization switches and cluch gears is thinkable, but this is all really cumbersome...

It's a bit ironic really, there's a bit of (trivial) circuitry in the 2x2 black brick before the wires of the LED lights split that causes the LEDs to work no-matter the polarization, because LEDs by their nature only work when the correct polarization is applied...

One solution would be to modify the circuitry in the 2x2 plate.

Schematics are here:
http://www.philohome.com/pf/pflights.htm

What basically needs to happen is that the diode bridge is removed and the C1 wire is soldered through to the + side of the leds (to the resistors) and the C2 wire to - side ...

Same for the other pair of leds but switching C1 and C2...