What the guide says about updating still applies. Updates while on A9LH + Luma are safe, and that people should stop asking about it. It is rather unfeasible that Nintendo would be able to develop a patch that uninstalls A9LH without bricking the system, so you should assume that new updates are safe by default. Just get on GBATemp and look at the subforums .. Do you see countless people complaining about bricks? If, then updating probably isn't safe. I doubt this scenario is ever going to happen, though.
Update your luma to 6.6 if you're not using it already, then you can update the FW. Download the updated CIA for HBL as well (though I really do have to ask .. why do people even use HBL? You can install everything that FBI offers as an CIA anyway). Also do NOT use Gateway on 11.3 - at all.. unless you want to lose A9LH. There's been reports of people losing A9LH while launching Gateway on sysNAND on 11.3.. Some claim these "reports" are false, but without someone willingly testing this and possibly bricking their console .. well .. yeah.