At a module level - no.
At a server level - yes, but currently on linux.
nwnx_haks allows you to 'hide' haks that are in your hak list, from All players, and only make it visible to certain players who indicate via a conversation or whatever, to say that they have the hak.
Once they do that, they are able to re-enter the server, and the hak is no longer hidden, which then enables the content for them - Which means that they can enter the areas requiring that content.
I dont use linux, so I have my own system in place.
I have my own application that downloads music, 2das, models, and entire tilesets via the application, and it installs it all into the override folder.
Override content can provide everything a hak can, except that it is sometimes considered more messy.
Eg- You have all the files uncompressed - filling your override with thousands of files, vs the one hak.
Players are then able to register on my forums, and fill in a profile field that indicates they are using the downloader content.
I use an API that allows my server to interact with my forums, so when a player uses an area transition, it automatically checks the persons forum profile if they have one, and if they say NO to downloader content, it doesnt let them in - as it knows that if they go in without the content, they will crash.
If they want to access, they need to select yes on their profile field - which is basically like a disclaimer I suppose.
They are selecting yes to indicate that they have installed all the content required, and its no ones fault besides their own if they crash due to not having the right content.
But yeah- if you wana make hak content optional, you either need to use nwnx_haks on linux, or use override on windows: unless someone can convert nwnx_haks to windows.