8.1. Any regional county municipality whose warden is elected in accordance with section 210.29.2 of the Act respecting municipal territorial organization (chapter O-9) may, by by-law, adhere to this plan for the warden. The by-law may, in respect of the person who is warden at the time it is adopted, have retroactive effect from 1 January of the year in which it comes into force. The by-law shall not be repealed, and no amendment made to it may have the effect of restricting the right of the warden to participate in the plan.