The only change is that AuReiNAND is now called Luma3DS. You do this by downloading the latest version of Luma3DS (I think it's now version 5.4), copying over the relevant files, and then renaming your payloads (Uncart/Decrypt9/Emunand9).
https://github.com/AuroraWright/Luma3DS/wiki/Installation-and-Upgrade
For the 11.0.33 U update, yes, it is safe for A9LH installed people to update sysnand. The only thing is that the new firmware locks out downgrading by putting in a hardcoded system titles, so you should have a working 9.2 sysnand backup if you ever want to get a "stock" system back. Oh, and if you use the cia version of Homebrew Launcher, you'd have to manually rename the payload on the card to reflect the new version of...