There's some way of completely blocking the update coming from wi fi?
(Without using router options? but only 3ds ones?)
I read somewhere that going into Wifi settings, then going to Spotpass and selecting "No" for both will prevent you from receiving updates automatically. It seemed to work on my 9.2 EmuNANDs. As for SysNAND, well, I've unlinked, and when I created my new profile, I selected "Later" when it brought up the ToS. I'm fairly certain Spotpass remains completely disabled until you accept (trying to change its settings pops it up again), though I haven't gone online in SysNAND just to be safe.
Oh guys, I have a question for you. I just bought a New 3DS XL (AUS) using the sysnand 9.0 so compatible with the Gateway. No problem about that.
But I still have all my saves on my old 3DS. I know that I cannot transfert the data from both console since the last sysnand is requested on both consoles, but what about a transfert with the old 3DS with the 9.4 update to the N3DS running with emunand ?
If your old 3DS is an Australian model, then yes. There are several accounts of people successfully transferring from SysNAND to EmuNAND, and vice versa. If it's not an Australian model, well, it's my understanding system transfer doesn't work cross-region. Actually, I'm not certain they both have to be Australian, but, if you can't at least pick the same country on both, you can forget about it.
However, you're talking about saves. System transfer is more about purchase info, NNIDs, and Miis. I think saves are only tied to your profile for genuine e-shop purchases, not ROMs and CIAs (well, ROMs converted to CIAs still save to the root, haven't tried any e-shop exclusives yet, mainly because e-ware in general always comes across as, well, leftovers -- if they didn't think it was good enough to cut it in the real market, there's probably a good reason).
Of course, for any game that uses firmware 6.x or higher that you've been playing on a 4.x system, the save is not properly encrypted, so, those will appear corrupt. Unfortunately, even a system transfer isn't going to fix them. Gateway's looking into creating a save tool I think, but it's hard to say when they'll be able to get to it. So, something like a Zelda: OoT save should copy just fine, but something like Zelda: ALBW probably won't. The only thing you can do is copy the .sav files from the root of the 3DS's SD card to your computer. Once the N3DS is exploited, copy them to it's MicroSD card. Then "see what sticks" as they say.
So my 3DS is on version 4.5 firmware, using my Gateway, but it seems to have downloaded a firmware update, and now I am worried I am going to accidentally click "A" at some point and fuck it up. This is while in Gateway mode. Is there a fix or anything or do I just need to be super careful? Assistance is very appreciated.
2Hack pretty much answered your question, but I would add that the 3DS usually will not start an update if it is not plugged in, so, as long as you're not charging it, it's also going to prompt you to plug it in, providing another opportunity to back out.
Unless it's possible to share saves between consoles by extracting the save file, I don't think you can. 
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K3Nv2:
