Section 72. In civil proceedings which are not governed by the Massachusetts Rules of Civil Procedure or by the District-Municipal Courts Rules of Civil Procedure, the parties may make agreements relative to amendments and the time for filing papers, which shall be equivalent to an order of the court to the same effect. Any order mentioned in section seventy-one may be entered by consent signed by the parties or their attorneys; but no agreement of attorneys relative to such civil proceedings shall be valid unless in writing.