I have switched monitors on laptops with different resolution and they just worked fine. Of course, as long as those monitor are "known" by the motherboard. Hence, my guess is that you can switch panel on the switch without caring about the variant. Backlighting is part of the display hardware.
It appears the backlight is on a separate ribbon cable on the Switch. But in all likelihood they didn't change the cables/connectors for the LCD, since it seems like a pretty minimal redesign.
In principle, is it possible to combine two switches (new series and unpatched one) in order to get an unpatched new unit?
As you may already know, there are two ways to hack a Switch, either through the RCM exploit which requires an unpatched SoC, or through software exploits like Caffeine which requires a sufficiently old firmware version.
Sadly, the SoC and NAND are tied together by the encryption keys used to encrypt the NAND being stored in the SoC, so you'd have to swap out both parts, which even if the old and new SoC are pin compatible, swapping out the SoC and NAND for an old model one would essentially just turn your new model Switch into an OG one.
Even if you could somehow get the keys from the new console, and re-encrypt the NAND of the old console (with a sufficiently old firmware version to be exploited, currently <= 4.1) to match that of the new one so you could keep the new SoC, you would run into issues with the fuse count not matching when trying to load an older firmware leading to the system not booting, nevermind that such an old firmware wouldn't have all the changes added to support the new SoC, and nevermind that by the point you have enough access to dump the keys you are already able to launch payloads anyway.
Since you can't downgrade a Switch even by physically replacing the NAND chip, and switching out both the SoC and NAND in this case would be rather pointless (even if it might theoretically work), the only way the new model Switch is ever getting hacked is if a new RCM or firmware exploit is found, or some sort of hardware exploit is discovered (think glitch chips on the 360)
I think it's likely to happen eventually, but for now anyone wanting to hack their new model Switch (or Switch Lite) will just have to hang on.
There's no way to cheat that, I'm afraid.