Distributing hack/code for groups feature

I’ve modified my install of WP to support user groups (which I called roles for some reason). Basically, you can assign users to be members of a group (one user to one group), you can then assign restrictions to categories based on these groups (multiple groups on multiple categories).
This then means that the posts in those categories will only be shown to users who are logged in and a member of one of the groups assigned to that category.
This involves a modification to a number of WP functions as well as a few mods to the database, so I can’t just roll this up into a plug-in.
I know that a feature like this has been requested, and I’m wondering how to distribute something like this.