Modification of a final judgment proceeds by supplemental petition, not motion (Rule 12.110), and requires a substantial, material, unanticipated change.
Support enforcement runs on records: due dates, amounts, arrears math. Civil contempt requires present ability to pay and produces purge conditions — punitive contempt is criminal territory (Rule 12.615).
Time-sharing and support are independent obligations: conditioning one on the other commonly proves impossible to enforce — and withholding reads as bad faith.