The order only requires that level of maintenance to be paid whilst the conditions are met. Once the conditions are not met the maintenance can cease - the crucial words are \"Payments continue until\".
You have to ensure that the trigger events have occurred though. Cohabitation can be difficult to prove if it's a case of the new partner moving in with your ex. It is better to give notice of your intention once the 6 months has been exceeded.
Yes, an application can be made to the CMS - the court has no jurisdiction over the payment of child maintenance