It should now again be possible to learn a rank 6 skill from your clan head mob. Say "show skills" for a list of the skills available to you, and say "learn <skill name>" to learn the skill. Clan skills will now show up in your list of practiced skills. They will also be automatically forgotten upon learning a new skill.
If you had previously learned a rank 6 skill, you will need to take a moment and get it again from your clan head mob. If you encounter any bugs, please let me know.