Hi Guys, a couple of years ago, I’ve modded an original 3DS (at firmware 4.2.0-9U) with the PastaCFW 1.2.1 (which I start by entering the DS profile on settings).
Now I want use the Luma CFW on it.
You don't have to remove your CIA's. They will work once you're on A9LH+Luma. Formatting will get rid of their tickets, but they can be easily re-installed later with Tikshop or the like. I'm not sure if you even need to format though; The guide lists two methods of booting into Decrypt9. One utilizes the DS Profile Exploit you're already using, but you should be able to overwrite it with the D9 launch. Then there's the browser exploit - If you have browser then you can just use that instead on your sysNAND and you won't even need to format.
Either way the 3ds.guide tells you everything relevant that you should know. If you're using emuNAND and planning to move into sysNAND only (which is what the guide instructs you to do), then make sure that once you boot into Decrypt9, you create a backup of
your emuNAND on top of the sysNAND backup that the guide instructs you to do. Then, after installing A9LH you get to "Restoring your system". Here you restore your system using "sysNAND Backup/restore" in Hourglass9, and restore your system using the
emuNAND backup. This will flash your emu into your sysNAND, effectively carrying over saves, tickets and other relevant stuff. Once you're done with the guide you can remove emuNAND from your SD card as it's now doing nothing but taking space.
Just make sure you're doing all of the steps on your sysNAND. Doing them on emuNAND would be completely pointless.
Also in case you're worried about losing the "safety net" that emuNAND brings:
1) You could keep using emuNAND at the cost of SD storage space
2) emuNAND provides no real benefits unless you like to use Gateway, as GW only works on 11.2. Launching GW on 11.3 will wipe A9LH from the console
3) A9LH loads before anything else so even if console is bricked - it's actually not. So long as A9LH is installed your console can always be restored through a backup.
11.3 FW and higher try to write into FIRM 0/1, which if successful, would wipe A9LH. This is why you always use CFW with A9LH such as Luma which protects the FIRM from writes .. So as long as you don't use something like the aforementioned "Brickway", you're good.