557. Any agreement under section 103 of the Real Estate Assessment Act, entered into by a municipal corporation or a school board and an undertaking subject to a decreasing tax under sections 99 and 102 of that act, remains in effect.
However, if, following such an agreement, an undertaking other than Hydro-Québec or one of its subsidiaries has, on 1 January 1980, paid to a municipal corporation or to a school board an amount greater than what it should have paid on that date under section 102 mentioned in the first paragraph and if an immoveable of that undertaking contemplated in that section must be entered on the roll under this act, the municipal corporation or school board in whose territory the immoveable is situated and which is a party to the agreement must refund to that undertaking such part of the excess as pertains to the immoveable.
Similarly, if, following such an agreement, Hydro-Québec or one of its subsidiaries has, on 1 January 1980, paid to a municipal corporation or to a school board an amount greater than what it should have paid on that date under section 99 mentioned in the first paragraph, the excess is deducted from the amount that it must pay under section 221.