Thanks again for attempting to explain things a bit. I couldn't find anything on memchunkhax2 - but do I need to, or was that just to help me understand? I still don't really know what emuNAND is, so could you tell me a little more about that and if you think it's something I'll definitely want?
I was looking into SafeSysUpdater (mainly this thread:
https://gbatemp.net/threads/wip-safesysupdater.409392/) and what I didn't realize is that the downgrade process is never 100% safe. Even if there's only a slight risk of me bricking the system, I'd rather not do it. The one exception would be if it would allow me access to the Japanese eShop somehow, and if that's the only way of doing it. Nothing else is all that important to me, and I'm happy just to have it working region-free.
By the way, I did get SVDT working and I'm very happy with it. The only thing that bothered me a bit (which may seem silly) is how ugly the icon was. I like everything looking nice and clean, which is why I downloaded SMDH-Creator back when I first got homebrew working on Ver. 10.1 - so I could make my own icons. Since I was only making it for myself, I just made it say "saves" instead of SVDT. In case you or anyone else wants to use it, I'll upload it here (I was going to upload the modified SMDH, but it won't allow it). It matches the colors I used with the gridlauncher version of the homebrew launcher...
It's no problem. memchunkhax2 is just the name of the exploit it describes; it was first discussed publicly during that hacking talk smea and a couple of other guys were in. It's not something you need to understand in order to get all of this junk working. Rather, the developers who made programs using it are the ones who need to understand it
If you're still interested, though, there's a thread around here somewhere that mentions the talk and gives links to it.
emuNAND is just what the name impiles:
emulated NAND. The NAND of the system is where all the system files are at. This is why messing with the NAND and installing things to it is considered risky - if something goes wrong, and something in the NAND gets corrupted, welp, maybe a brick. Now, if you're messing with emuNAND, no problem, even if things screw up. In sysNAND, if you installed a corrupted system file by accident, you're not going to have much luck recovering from that. But in emuNAND? No biggie, just restore a backup (always backup before you install something potentially risky and you're good). Think of it in terms of emulation and Pokemon games: if you performed certain glitches in Red/Blue, like the ZZAZZ glitch and messed up a step or saved at the wrong time, your cart became useless for regular play. But in an emulator, you just need to reload the ROM.
I say all of that to say it's basically a safeguard and a playground for anything hacking. emuNAND is the first choice for most people who use custom firmware to load, as you can load custom firmware with sysNAND, but you know. As for if you want it, it really depends on what you're looking to do with homebrew and your 3DS. Exclusively, those with emuNAND+CFW can install unsigned .cias (think faster running homebrew, VC injects, non-legit .cias, etc.), and maybe a few other minor things. It also makes some things easier, like cheating in specific games (the NTR CFW has a plug-in system that allows you to do this). What I use it for is mainly homebrew games that have .cias, GBA VC injects and other VC injects. Since most of my media is physical, it generally doesn't matter what system version I'm using.
For what you seem to want, it might be the thing for you, since you said you might want to access the Japanese eShop. Personally I don't know a way that it can be done, as I don't understand why you cannot already (unless you just mean access the eShop at all). While eShop access is possible on lower firmwares, you couldn't access it in the first place unless you were on <=9.2. And if you were on <=9.2, you'd just set up emuNAND and update that. The easiest way is to just get your emuNAND to the latest firmware, as all CFWs out there support 10.5 emuNAND on either 3DS.
If you choose to downgrade, read up on those threads that talk about it a lot (even if they're like 50+ pages; knowledge is your best asset here). You're right in that it's never 100% safe as you read, but there's a better version, even, than safesysupdater. See, safesysupdater is based on an older version of sysupdater that was modified early into the whole downgrading hype. Sure, that version could work, but if something went wrong, there's a very good chance you'd have a hard brick. Later on, other versions were made to take this into account. The earlier build(s) (TuxSH's) uninstalled
all the files first, and then installed all the update files. The later build(s) (julien20's) first installed all the version relative safemode titles first, then uninstalled
one title, then installed the version relative version of that title, rinse and repeat. So with julien20's version, while there's still a small chance of hard bricking your console, to my understanding most of that is due to user error and not the program's error. Regardless, do a lot of research before you make your decision - this is a good thread to read when you have the time:
https://gbatemp.net/threads/simple-guide-to-downgrading-your-3ds.407888/page-133
Also, glad to hear you got SVDT to work. Nifty little thing, ain't it?