Authority for entering into agreements pursuant to this chapter shall be construed as supplementing existing authority for legislative bodies of local agencies to enter into agreements for the providing of municipal services and functions and shall not be construed as authorizing the legislative body of any local agency to enter into an agreement for the providing of municipal services or functions which it is prohibited to provide by law or which exceeds the force account limit applicable to the local agency contracting to receive services.

The amendments to this section which become effective January 1, 1981, shall not apply to any agreement which was made prior to that date nor to the current term of any self-renewing or renewable agreement which had been entered into prior to that date.