It's safe, I do this a lot, my friends do this. Have mostly all my friends on A9LH+Luma3DS CFW SysNAND by now.
Also, if you're on 11.0.0-33, you shouldn't be getting any update nags, you might have seen an update notification, but I've only ever seen this on a couple of the systems, I've done, and just usually a message that shows up on Spotpass, and nothing more, it's not really a nag. And it'll probably be a good while, before the next Nintendo Stability Update, and when that hits, just come back here and see how that turns out.