Where immediately before the appointed day, the Union or an existing State is a party to any legal proceedings with respect to any property, rights or liabilities subject to apportionment under this Act, the successor State which succeeds to, or acquires a share in, that property or those rights or liabilities by virtue of any provision of this Act shall be deemed to be substituted for the Union or the existing State as a party to those proceedings, or added as a party thereto, as the case may be, and the proceedings may continue accordingly.