Can a costs order already made be set aside or varied later in Ontario family court?

It's possible, but it isn't routine — a costs order, like other court orders, is generally treated as final once made, and a court won't simply revisit it because the paying party later disagrees with the amount or has a change of heart. Setting aside or varying a costs order typically requires showing something specific went wrong, such as a genuine error in how the order was calculated, new and significant information that wasn't available when the order was made, or a procedural unfairness in how the costs decision was reached.

The route for challenging a costs order also depends on the circumstances: in some cases, it may be addressed through a motion back to the same court, while in others, particularly where the complaint is about the judge's substantive reasoning rather than a clear error, an appeal may be the correct process instead. Because these are two different procedural paths with different requirements and timelines, and because courts are generally protective of the finality of costs decisions, anyone wanting to challenge an existing costs order should get legal advice quickly on which route actually fits their specific complaint, since timing can matter significantly.