Good find, that's a great source, the thread shows some good wiring tricks and how to alter the display by switch and relay, different bulbs too. I would still like to change my green displays to blue, but that is a lot of work and some is easy, other items are really tough.
For your use though, just to be able to run the lights during the day, why not instead isolate the one headlight circuit from the rest of the lighting? Since you want to leave the rest of the lighting working as stock, I'd leave that part alone, and go to the wiring that turns on the head lights, and interrupt that. You can keep the normal interior lighting working as it is, and use an alternative method to turn on the headlights, or just the running lights, when you want them on(without affecting the interior etc). I'm saying don't use the dash headlight switch to turn on the external lights you want on, use another trigger for them, and a diode as needed to keep from back feeding the untouched lighting circuits.
I used the oil pressure dummy light circuit for my 99 truck, just one wire to trigger my headlights. But I didn't isolate that from the rest of the lighting, so I'm sure it means that my interior lights dim during the day when the headlights are on. That hadn't bothered me, but I guess I should take a look at that again and see if it needs some further modification. I went into the trigger wire from the light sensor on the dash, and cut it there and substituted the oil pressure sensor signal. It's been since 2006 that I did that, so I've forgotten where exactly that was. I made tons of wiring changes, so that one was minor and I don't recall many fine details.
Keep brain storming, it's cool to see what you and others think of.