There is always a risk when modifying FIRM0/1, but the safeA9lh payload is much more stable than the homebrew version used when installing A9LH for the first time.
I've updated twice now, always sticking to the plailect guide and downloading the official safeA9lhinstaller and a9lh from the official github releases.
I had a friend name the payload start_safea9lhinstaller.bin, but DO NOT DO THIS as once you enter the payload the start is used to uninstall and if you are on 11.1 you just lost cfw (he lost it!).... Name it like the guide says down_safea9lhinstaller.bin.
Here is link to updating instructions:
https://github.com/Plailect/Guide/wiki/Updating-A9LH