You cannot grant freedom to your headquarters. Fortunately, you can delete all of your defensive armies (at any time
) which will get rid of the HQ if this is your last sector. (unfortunately, this does not give you any goods like granting freedom, and the original NPC will take over the sector again with its default armies) Your HQ will automatically move to another sector if you still own one in that province (and the same would happen if a guild successfully conquered your HQ)