The 2019 uses a very sophisticated CanBus system to run pretty much everything. Gone are the 2018 and older days where you can just "splice" into the harness. Think of trying to splice into a USB cable.
Even if you drilled and mounted the roof lights, you would have to get the CanBus harness to communicate with the truck's computer, and have the computer flashed to authorize those circuits. If you bypassed, the system will see an unauthorized power circuit and either switch it off or trigger a warning light.
Get it with the lights factory if that's what you want. You won't be happy with the headache of trying to get them to work afterwords. 2018 and older yes, easy. 2019+ need CanBus controller.
Also if you do plan on adding anything electrical to the vehicle after it's built, I highly highly
recommend you order the AUX switch panel when you order from the factory. It gives you 6 monitored circuits that you can tailor to your demands.
To get an idea of what your in for with a 2019+, see this product on this website called HexEZCan
that I had to use just to add extra lights to my 2017 CanBus motorcycle.
Is the circuit of five roof lights on its own CANbus controller ... or are the five roof lights simply wired into the existing running light power circuit? I doubt that the running light circuit is intelligent enough to throw a code when it's sourcing an extra 3 to 5 Watts... and I doubt there'd be good reason to provide a unique CANbus controller for a circuit that's always activated when an existing circuit is
. I could be wrong... but there's no good justification for either of those scenarios. That would be like having separate CAN controllers for each of the three rear brake lights. Were I laying out that subsystem as an option -- and I have laid out similar arrangements for other vehicles -- I would provide a convenient 1-way power connector in the common harness that the optional roof wiring would plug into. It's minimum cost and minimum impact, and as we all know, FCA is all about minimizing cost.
It's actually relatively straightforward to splice into a CANbus data line mechanically. A working CANbus ladder is already terminated successfully, so all that's necessary is running shielded taps into both sides of the twisted pair close enough together so that you don't introduce noise into the pair at the junction, and then twist the new branch generally 11 to 13 twists per inch using a pair of 18 to 22 AWG automotive wires ... or a pre-twisted made for CAN twisted pair. You would then route that new twisted pair to your new device. Assigning an address to the new node, and configuring your network controller to issue commands to that address, are, of course, an entirely different matter.
If you want to add entirely new devices and bypass the computers entirely, you can always run a fused line directly from the battery, or a fused line from the hot side of the PDM, before the computer starts messing with the outputs, and use your own switches in the new circuits. You know... the way we all did when we added fog lights to our first cars when we were 16 or 17. That will still work just fine.
As you've noted, if you're trying to add something that's built into a unique CAN-enabled PDM's output pre-designated for that function, then, yes, you need to activate the option and make sure the controller is on the network. But the roof lights aren't a unique function. They're almost certainly wired into the existing running light circuits.
But... I could be wrong. Wouldn't be the first time.