Now I'm wondering why not just buy the flashlight that has the wanted or/and needed output of power, light and whatever else your would be changing. The technology and parts are there because someone is doing it. Don't buy a mazda and expectto turn it into a corvette. Wait a jeep and expect a hummer....Wait for it llllllllllllllllllllllllllllllllllllllll
But then it clicked really like the high performance of upgrades but still like the look of old school
The concept is sound, but, the reality of it is that that stock light you suggest as an alternative doesn't exist.
IE: If you buy a light with similar performance, it will typically be a lot larger, and, therefore not an apples and apples swap.
For example, the highest throw stock light within the "flashlight" form factor is the Olight SR95UT, with ~ 250k cd.
Vinh makes lights smaller than that with ~ double the cd. There IS NO stock light that has that performance...in that form factor. That means there IS NO stock light you can order instead of a modded light to get the same performance.
For some of the smaller lights, say single 18650-ish, etc...sure, you could replace a light that goes on your key chain with a 3D mag light sized replacement, but, really, IS THAT a replacement?
As for modding Jeeps and Hummers, there is a HUGE market for those DOING THAT. People take a stock Jeep, and modify it so it can do what they want it to...because they can modify the Jeep to go where the Hummer can't. People also modify their Hummers, so they can go where stock Hummers can't, and so forth.
No matter how much you modify a Hummer, it can't get through trails that are too narrow for it....but not too narrow for a jeep. This is analogous to flashlights...in that size DOES matter. If its too big to carry with you, you won't have it when you need it, and, all else being equal, you are more likely to be able to carry a smaller light than a larger one.
If you need a certain combination of UI and output, the modded light can give it to you in a smaller package.
So, that's why people buy a modified light instead of a larger and typically a lot more expensive stock light.
:D