Not necessarily, one needs only to renounce his Witch Hunter title and duties. Witches are generally described as solitary and don’t need to form groups (they always worked alone during school projects). Besides, most witches are women and women can’t stand each other.
Actually I’m being half-serious - I would like some more lore to explain the nature and role of witches and Witch Hunters in Cairn. My expectation is that witches were formerly the only ones using witch powers and anyone using those powers would be considered a witch. They became enemies of the state through some form of criminal activity such as abducting children or simply not paying taxes. The Imperials formed Witch Hunters (synonymous with Inquisitors perhaps?) to…hunt them. These Witch Hunters quickly realised they would not be effective if they didn’t know the witch arts themselves. So they learned them. At this point the definition of witch would have changed to those using witch powers but are also enemies of the state. Meanwhile the Witch Hunters remained law-abiding taxpayers.