Upon approval of such agreement, evidenced by execution thereof by the department of revenue and the person so agreeing, the agreement shall be final and conclusive as to tax liability or tax immunity covered thereby, and, except upon a showing of fraud or malfeasance, or of misrepresentation of a material fact:
(1) The case shall not be reopened as to the matters agreed upon, or the agreement modified, by any officer, employee, or agent of the state, or the taxpayer, and
(2) In any suit, action or proceeding, such agreement, or any determination, assessment, collection, payment, abatement, refund, or credit made in accordance therewith, shall not be annulled, modified, set aside, or disregarded.