452.415.  When sections 452.300 to 452.415 shall apply. — 1.  Sections 452.300 to 452.415 apply to all proceedings commenced on or after January 1, 1974.

  2.  Sections 452.300 to 452.415 apply to all pending actions and proceedings commenced prior to January 1, 1974, with respect to issues on which a judgment has not been entered.  Pending actions for divorce or separation are deemed to have been commenced on the basis of irretrievable breakdown.  Evidence adduced after January 1, 1974, shall be in compliance with sections 452.300 to 452.415.

  3.  Sections 452.300 to 452.415 apply to all proceedings commenced after January 1, 1974, for the modification of a judgment or order entered prior to January 1, 1974.

  4.  In any action or proceeding in which an appeal was pending or a new trial was ordered prior to January 1, 1974, the law in effect at the time of the order sustaining the appeal or the new trial governs the appeal, the new trial, and any subsequent trial or appeal.