<blockquote><blockquote><tt>(a) the order replaces the part of the agreement that provides differently for the same subject matter, and</tt></blockquote></blockquote>
<blockquote><blockquote><tt>(b) the remainder of the agreement remains effective.</tt></blockquote></blockquote>
==Changing orders about custody==
A 1996 case of the Supreme Court of Canada called ''[http://canlii.ca/t/1fr99 Gordon v. Goertz]'', [1996] 2 SCR 27, sets out the factors a court must consider when hearing an application to vary orders for custody or access made under the ''[[Divorce Act]]'':
*The parent applying for a change in the custody or access order must first prove that there has been a material change in the circumstances affecting the child.
*If this threshold is met, the judge on the application must make a fresh assessment about what is in the best interests of the child, considering all of the relevant facts relating to the child's needs and the ability of each parent to satisfy the child's needs.
*This assessment is based on the findings of the judge who made the previous order, as well as the new circumstances.
*The assessment does not begin with a legal presumption in favour of the parent with whom the child mostly lives, although that parent's views are entitled to great respect.
*The focus is on the best interests of the child, not the interests, rights, and entitlements of the parents.
In other words, the applicant must show that there has been a serious change in circumstances that affects the child's best interests before a court will even consider the application. Once this hurdle is crossed, the court will look at all of the circumstances before making a decision, as if the case was being heard for the first time. Most importantly, this means that there is no automatic presumption in favour of the status quo.
Cases where an order for custody has been varied include circumstances such as where:
*The change is in the best interests of the children in the long run.
*The parent with the children's primary residence has attempted to alienate the children from the other parent.
*The parent with the children's primary residence has repeatedly frustrated the other parent's access to the children.
*The child has been apprehended by child protection workers.
*The child has been abused by the parent whom the child primarily lives with.
*A mature child has expressed a wish to live with the other parent.
The courts are unlikely to change custody where the children are happy in an existing stable and secure setting.
<span style="color:#D2691E">'''Important changes'''</span> <br />
Under the changes to the ''Divorce Act'' that took effect on 1 March 2021, "custody" is now known as ''decision-making responsibility'' and "access" is now known as ''parenting time'', for people who are or used to be married to each other, or as ''contact'' for other people.
==Changing orders and agreements about guardianship and parental responsibilities==