I've successfully uninstalled TWL_FIRM and DS Cart Whitelist from sysnand and installed TWL_FIRM and DS Cart White list from v2.0 initial scan versions from CDN (basically installed the oldest available versions on CDN). Appears to work. Though only DS flashcart I have is the Gateway Blue card so I can't really test that. It still works on my 9.2 sysnand after this so I assume this worked correctly.
So in theory anything that worked on 2.0 FW will now work on 9.2 which is what my sysnand is currently on.
I'd install the v1.0 TWL and DS Cart White list, but those aren't on the CDN. 1.0 launch FW isn't on CDN. Is it even possible to dump TWL to a CIA file like you can most other system titles? That's the only way I see 1.0 TWL becoming available to the rest of us. I emplore those who still have a 1.0 launch console to do this. That's assuming you have it nand modded and have a backup of your 1.0 launch FW that you can boot as emunand...if that is even possible.
Either way this appears to be safe. So if you are looking to downgrade TWL/DS Cart White list for better DS flashcart white list on 9.x sysnand. You now have a way to do it.
However for n3DS users:
Do not attempt to downgrade TWL_FIRM! n3DS has it's own version of TWL and the old 3DS version is NOT compatible! You can downgrade TWL on n3DS, but only to the oldest available version which is the one that came with 8.1 for Japan consoles and 9.0 for USA/Europe consoles. Installing 2.0 TWL from classic 3DS on N3DS will either brick it or break TWL!
DS Cart White list is not it's own version on n3DS. So you can still uninstall that from n3DS. Heck I wonder if you even have to install 2.0 DS Cart White list. Just uninstall it and be done with it.
EDIT:
Actually after further tests....Don't leave the DS Cart White List uninstalled. Oddly a "broken" one works (the version where people spoofed the version string and broke the signature), but if one isn't present at all, TWL won't boot. Even my legit DS games wouldn't boot.
So be sure to have some kind of DS Cart White list installed or DS games won't boot. Preferably the v2.0 (v1.0 if you have a way of dumping it from 1.0 FW).
Also I've uninstalled the following apps from sysnand without any adverse effects:
Health & Safety
Nintendo Zone
AR Games
Face Raiders
Mii Plaza
(refer to
http://yls8.mtheall.com/ninupdates/reports.php for title IDs of the above mentioned apps. Note that some may have different title ids depending on your region of console)
I did this to help it boot up faster as I never use those. I will keep them on emunand however as I might find a use for one or two down the road. Emunand is where all my games live. Sysnand is just there so the console can power up.
Heck I could probably uninstall some applets as well like the friends list and Mii zone. I could also remove Activity Log, the audio player, and camera/video player app. But the camera applet might not work correctly without the camera/video player app and I may still use the camera applet for it's QR scanner. Obviously the Web Browser would stick around as well.
The audio player I will just keep there incase I want to bootup and just play some music. Especially if I'm on the road trip or something.
In either case, the above list of apps I have tested the system with them uinstalled and everything appears to still work. I don't know if this causes issues with playing games in sysnand. But the only game I may use in sysnand is Cubic Ninja and I did test that one as well and the Ninjhax exploit still works so that is all that matters for me on sysnand. Note n3DS may have different title IDs for certain apps. Especially those that have features only available on the n3DS.