No, adding a relay to slot 4 won't get you DRL. For one, there are several relays providing DRL, and for two, the wiring isn't there. I believe US and Canada use the same body ECU, so I don't know what 'tells' the ECU to operate DRL, other than possibly the presence of the ambient light sensor.
I don't know what PTC stands for. I don't think PS stands for power steering, but I don't know what that stands for either.
Repair manual for 2004/2005 doesn't mark that DRL relay for RR Fog. Other markets I believe have rear fog lamps.
CHS W/P = Coolant Heat Storage Water Pump.
I don't think the electrical aspects of the car's lighting has changed for 2006, only the style of the lamps themselves. But I haven't gotten around to downloading the 2006 stuff.
Ah, found PTC. PTC = Positive Temperature Coefficient.
From what I can surmise, the PTC heaters are in the heater core and activated together, whereas the PS heater is in the air duct, and can be activated separately.