Katner,
Yes, you can rewire your DRLs into your fogs if you want. And yes, they stay on all the time, unless you apply the hand brake.
What I did on my 5, is to let the wiring as it is, and simply install HID on low and fog lights. The only thing I have to do ( and this means alot of thinking at first sight) is to turn on the lights BEFORE starting the vehicle.
So... First thing I do, is to turn on the lights, then put the key in the ignition. Therefore, I have both sets of HID working, without having the HID to fliker all the time. The only downside with this, is when I bring the car to the garage... Cause they don't know. Altough.... I have been running the M-5 like this since a year now and guess how many times I had to go for an oil change and minor fixes... And nothing happened...
So it's up to you! Keep us posted buddy!
Jasma