Hey argleargle,
Couple of things to help out. On the automotive side of things, changing a light source is a no no, as you found by poking around the forum. Exterior lighting is regulated and needs to conform to certain requirements. These assemblies are designed to work around a certain light source. Changing the light source, ie from filament bulb to LED with filament bulb base totally nullifies the optics at work in that assembly. That is before you even bring the lens into play. Some examples of this, the previously mentioned 3497 is a legit upgrade over the 1156 because the filament shape, size and location that the optics see is the same for either bulb. Placing a rebased HID or LED bulb into a filament based lighting assembly is a no-no, however, because the optics see a completely different shaped and position of light source, and thus are no longer able to create a properly shamed beam as they were before. The second thing is, the DOT doesn't "approve" anything. They have their standards, and it is up to a supplier of products to self certify that their products meet these standards. So "DOT approved" is a red flag. "DOT compliant" make more sense, but in the case of a lot of overseas/el cheapo/fly-by-night/(insert adjective here describing cheap crap) suppliers, they will stick anything on the packaging to help them sell their junk, and unless a serious accident which brings a certain product into the line of fire, they usually get away with selling that kind of stuff for a while.
So, there are definitely legal and effective upgrades available for car exterior lighting, but not as many or as easy as the internet, sites like ebay and other forums would have you believe.
As far as how friendly this subsection is, as I noted previously, headlights (exterior car lighting in general, in fact) arent like flashlights. Changing a flashlight bulb "shouldn't" hurt anyone, and moding is kind of no holds barred, lets see what we can do! Headlights have to provide adequate illumination for the driver while not blinding others, while standing up to a pretty severe service condition. They have hundred of thousands of hours of engineering done by professionals to achieve this. This is why any modifications to a cars exterior lighting, which is a regulated safety system, must be approached cautiously and with thought. Sadly, many forum goers sign in here, ask our moderator, who is an industry expert, as well as a few other very knowledgeable experts for advice, and then have a tantrum when they are told that their HID's are illegal or whatever. Given the effects on safety that illegal mods can have and some peoples attitudes, this forum can be somewhat terse at times, but the advice given out is first rate and is always in the asker's best interest, if they are only willing to take it.
Cheers
Dave