Here is my suggestion.
First, choose a silhouette for your fixture (the shape), and morph its edges for your desired look. and then choose the shape of the lights inside (square, circular, ovular) and then you can just move them around inside the silhouette as you please. Then, save it as your own fixture to be used on other cars.
For example, let me describe the process for this BMW headlight.
In blue is the silhouette. This is the headlight’s shape, as described previously, and can be edited by moving the darker dots’ positions. These are the “edges.”
Shown in orange are the lights. These are prefabs and should have different variants for each type (round, square…) You could also make your own variants by editing each part of the fixture’s material to your liking (eg. making a specific part chrome)
Finally, in green, are the indicators. Their shape can also be edited via its edges. These indicators can also be used as “headlights” if that is your desire. For example, if you wanted to make a headlight with only LED strips as lighting (cough, Lucid Air, cough,) you can. It’s supposed to be your unique design, anyway.
This would be a way better way of having a distinct style for your brand, rather than downloading a mod of your choosing or spending days trying to model a fixture yourself, especially at the level of detail of the headlight above or as a beginner.
The only question is if this is actually doable, or if the car’s aesthetic customization is as important as the car’s mechanical customization.