No downgrader is without fault, there is always the risk of bricking. I've used every downgrader since the very first alpha one was made for 10.3. Personally I find SafeSysUpdater, comes with the least amount of risks.
Check this tutorial, you don't need to use all of it but section 2 is dedicated to downgrading to 9.2 and if you follow every step correctly you should be good.
Edit: I'm dumb and forgot to link but I was referring to the tutorial the user below linked!
I have an old 3ds xl on firmware 7.2.something, trying to download maps in fire emblem awakening..
it says it needs system update. is that hard to do without bricking? dont want to update too far..
I used PlaiSysUpdater yesterday and it worked perfectly. It's a no brainer downgrader that checks if the update files are safe before attempting the downgrade. It downgraded my 10.5 New 3DS via menuhax.
I use SafeSysUpdater (did four 3DSes) - it checks for version compatibility.
Also, highly recommend PlaiSysUpdater because it can do both the 9.2 and 2.1 (if you are doing the AL9H exploit), and can save you a few steps of locating software...
Finally... My decission was Safesysupdater. Anything well without being that in the first two hours after the DG,the console toke randomly a few times more than 2 minutes to boot.
Thanks.