It also somewhat depends on whether stock auxiliary lights are designed for fog use (low, wide beam directly in front of the car), supplementary driving lights (normal height beam pattern to fill in and supplement the conventional low beam directly in front of the car) or if the automaker put them in for primarily appearance and marketing reasons and they don't work great for either. I almost never use mine on the Focus ST but they seem to be a combination but lean more towards the supplementary driving light for the low beam rather than a true, fog lamp that keeps an extremely low beam pattern to reduce glare reflection off fog, snow, and rain and designed to be used at slower speeds under poor driving conditions.
Just some random thoughts since on older thread posts, for those in the US market that want a little added safety/visibility the daytime running lights provide (studies have shown around an ~5-7% reduction in multi-vehicle frontal collisions for models equipped with DRL compared to those without), I'd have to skim over the shop manual but wouldn't be surprised with the requirement for other markets if it is an option that might be enabled in the GEM (general electric module, i.e. body computer) programming.
If someone want to use the driving/fog lamps instead and come on every time the car is running, it wouldn't be too difficult to rewire the lamps and power them off a relay connected to a fused battery source off the underhood power distribution with the relay activated off a switched ignition source. As for LED conversions, the quality of the actual light emitting diode used to include factors such as output, color temperature binning (e.g. selection and control over the different color temp so when ordering a warmer yellow LED you actually get that color temp), the lens used (integral on the chip or external) as well as the electronics driving it and heat sink used all play big parts in how effective they are. While being slightly more energy efficient as xenon HID bulbs on a lumens output for watt power consumed, those other factors play a big part in how well an LED works in an actual, specific application.