After the creation of a joint agency, any other governing body may become a member upon:
Any member may withdraw from a joint agency by resolution or ordinance of its governing body. All contractual rights acquired and contractual obligations incurred by a member while it was a member shall remain in full force and effect.
Notice of any change in membership shall be filed in the office of the Secretary of State and no change shall be final until such filing.
S.C. Code § 6-16-70