I found a "splitter" that plugs into my stock 4-pin and then splits into 3 more 4-pin outlets.
One like your thinking, I use for my license plate light, one for my multifunction light on the roof rack and the last if needed, for anything else.
For my aftermarket reverse lights, I did the traditional tap from the factory reverse light and then used it as the trigger for a relay. I also have a separate manual switch wired to the same trigger on the relay to manually turn on my aftermarket backup lights when needed. I added a diode on the reverse light trigger lead to isolate my wiring from the vehicles just to be on the safe side. I'm not used to "computer" vehicles Lol.. so I have tried to isolate all my electrical work from the Jeeps.
Embedded LEDs... sounds great !