This has only been tested by myself on a small, old 3DS on 8.1, 9.0 and 9.4, but it's reasonable for this to work on any console. Feedback is obviously appreciated!

1. Completely power off your system.
2. Boot in recovery mode (press L+R+A+↑+Power, hold the first four about 1 second, more won't hurt the system but only your fingers... )
3. It will ask you as usual to update. However, it will take a little longer for the screen to come up compared to the speed it would have had if you didn't already have an update.
4. If you click yes, the update will be completely redownloaded then installed...
5. If you click no, it will power off and you'll go home free!

Update 2017: Yes, this is only for sysnand (although you can hack the import.db of a nag-free sysnand's internal storage onto emunand through Decrypt9 or similiar ways, check out specific tutorials), because no CFW implements the launching of emunand's recovery mode!

This is also unrelated to the forced updates for YouTube or the browsers bundled with 9.9+, and neither it resets the "update available for this app" text
on the Home launcher!

 

[JoostinOnline]

After 48 hours, the nag to update hasn't returned on my 9.2U 2DS, so thank you OP.

It shouldn't as long as you don't have the 3DS connected to WiFi while it's in sleep mode (closed).

 

[DjoeN]

Put in a game and decided to download the update for that game (SMB or was it MH4)
So i unticked my Nintendo webrestrictions on the router so i could access the nintendo servers
Decided in the end, not to do it, but i got the update nag, every few power on i got the nag screen
Ticked back to block the nintendo website restrictions in my router (this way i can streetpass and have internet access (youtube and browser) but no eshop access and no system can't get updated (if you try it gives a connection error)
Nag screen kept popping up every now and then (daily), so did this trick and for 7 days now, no update nag to see

I keep WiFi enabled on all my 3DS systems for my Pi streetpass relay, but only when i have my Nintendo website restrictions enabled. (Yes, there in sleep mode with WiFi on, No i don't get any updates over my Pi streetpass relay)
My N3DS and 2DS are on 9.5, so whenever i need to access eshop, i have to be sure to turn off wifi on the other systems and disable website restrictions on my router

 

[Pedeadstrian]

Could someone try if the browser works after removing the nag?

Why wouldn't it? If it worked before, it'll still work. But, since you'll be connected to the internet, you may end up with another nag.

 

[Shady Guy Jose]

It's a gamble, I went to 9.3 and on since I wasn't going to buy Cubic Ninja but we all know what came out afterwards...

It was well known that we shouldn't update to 9.3 a long time before the new gateway exploit came out... They even had a news post on their website just for that...

 

[DjoeN]

Why wouldn't it? If it worked before, it'll still work. But, since you'll be connected to the internet, you may end up with another nag.

If you block some sites on your router (firewall settings) you don't have to care about getting the update nag and still be able to access youtube and internet (no eshop or game updates or theme's buying)
Look at a post i made in another thread for a screenshot of my firewall/website restrictions settings.

 

[Slushie3DS]

Wow, this is incredible! Good work, and thank you for your documentation!

 

[Arecaidian Fox]

Confirmed to work with my 9.0U N3DS.

 

[mid-kid]

I tried this on my 4.5E old3DS, but I keep getting it again when I connect to the internet, even though I've configured OpenDNS correctly according to this thread.
It doesn't when I don't connect to it, though.
Anyone else having the same problems?

 

[Dycedarg]

If you block some sites on your router (firewall settings) you don't have to care about getting the update nag and still be able to access youtube and internet (no eshop or game updates or theme's buying)
Look at a post i made in another thread for a screenshot of my firewall/website restrictions settings.

If I block those sites in my router, will I still be able to go online inside the game I'm playing? Like do online battles in Pokemon.

 

[Ryccardo]

If I block those sites in my router, will I still be able to go online inside the game I'm playing? Like do online battles in Pokemon.

It should (of course this ignores the problem of getting game updates)

 

[Dycedarg]

It should (of course this ignores the problem of getting game updates)

Cool! Thanks!

 

[Osmosis]

Wish I had known this a while back... and that GW tools works on 9.2 or lower. Really, the two should be top sticky post for new users.

That way they will block FW update long enough to make a backup of firmware and ROMs before anything happens.

 

[d0k3]

Wait, the 3DS has a recovery menu?

I wonder why no one has tried to exploit this so far.

 

[Ryccardo]

I wonder why no one has tried to exploit this so far.

As I previously guessed:

• The existence of this feature was only documented on 3dbrew, which is hardly a website with nicely laid out facts
• People who care about not getting updates will most likely not play with a feature whose only official effect is to [re]download and install them (if you were wondering, it can also get you to network settings without knowing the password, if you locked your console)
• People who had no problems with updates clicked yes/didn't notice the effect/didn't bother to report
• The update nag is no big deal (in fact the worst part is getting the blue light daily) -- to actually install updates you must press A or touch an onscreen button then touch another (so even if you were mashing A and it popped up, uhhh you can tell apart "Agree" and "Not Agree" I hope)

 

[powersaver]

Hi, anyway to use this method to update via game cart? Thanks for the info.

 

[Ryccardo]

Hi, anyway to use this method to update via game cart? Thanks for the info.

Hm? Card updates to sysnand will work as always (updates only core OS and Home launcher, region locked) and this tip doesn't influence card updates at all...

 

[powersaver]

From what I gathered in another thread, the method discussed here is a safe-mode method and can be used when there is a partial brick/black screen.

Does anyone know if there is a way to use this method to update via game cart?

Hm? Card updates to sysnand will work as always (updates only core OS and Home launcher, region locked) and this tip doesn't influence card updates at all...

 

[Ryccardo]

From what I gathered in another thread, the method discussed here is a safe-mode method and can be used when there is a partial brick/black screen.

Does anyone know if there is a way to use this method to update via game cart?

Well, it's true that this runs in safe mode (meaning an alternate kernel), but I doubt this alone can save you from any brick (MAYBE MAYBE Nintendo sets a proxy that redirects the update server to properly signed Home-replacing service tools? heh), and for all I know card updates are managed by Home only...

 

[Dan-the-Rebirth]

how do i get rid of the update nag on emunand? without reformating i mean^^

 

[Ryccardo]

how do i get rid of the update nag on emunand? without reformating i mean^^

You can't, at least not in a practical way...

I've compared dumps of 8.1 before and after downloading 9.5-23 (or was it 9.6?) -- a lot of files are added without an obvious naming rule, and worse some are even deleted, so with current knowledge any (currently nonexistant) tool to undo update nags must be programmed case by case (and a case is an exact "now installed/to avoid" pair)!