Although 'terms' isn't the translation of 'medidas', I think this is what I would use.

Custody and child/spousal support terms are binding, but they are not set in stone. In most states, the court order for a change is called a “modification.” Technically, you can pursue a modification at any time after the last order. The key is knowing when you have enough evidence to convince a court that a “substantial change of circumstances” has occurred since the entry of the original order.

https://expertbeacon.com/modifying-divorce-decree-child-cust...

Post-judgment modification of divorce terms concerning custody and parenting time can also be necessary if one parent or the other plans to move to a new ...

http://www.moserpa.com/Family Law Info.htm

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Note added at 20 mins (2016-09-02 14:58:59 GMT)
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Loss of employment, relocation and income level are common reasons for seeking a Divorce Modification through a court order. Our experienced attorneys can assist you with submitting a modification of divorce terms or in fighting one.

http://oceancountydivorceattorney.com/divorce-lawyer-ocean-c...

I think my answer is better suited for the US, not the UK.

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Note added at 43 mins (2016-09-02 15:22:31 GMT)
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You could replace 'terms' with 'arrangements'. Up until 2014, a 'statement of arrangements' existed in the UK.

As of the 22nd April 2014, it has not been necessary for a Statement of Arrangements for Children form (also known as a D8a) to be filed along with a divorce petition if any minor children were born to, or lived with, the Petitioner and Respondent.

Previously, it was necessary to file this document in order to show the court that appropriate arrangements were in place for any minor children that would have been affected by the divorce. Due to recent changes to family law, however, Section 41 of the Matrimonial Causes Act 1973 – which stipulated that the courts were required to consider whether or not it was necessary to exercise any of the powers afforded to it by the Children Act 1989 within divorce proceedings – has been repealed. As a result of this, the court is no longer required to consider whether appropriate arrangements are in place for the children of a divorcing couple; hence why it is no longer necessary for such a form to be submitted when the couple file for a divorce.

http://www.quickie-divorce.com/blog/2014/05/28/why-a-d8a-for...

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Note added at 54 mins (2016-09-02 15:33:09 GMT)
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I've found what I was looking for! The British 'statement of arrangements' has been replaced by a 'child arrangement order'.

Sometimes circumstances change after the court has made a final decision. For example, the arrangements in a Child Arrangements Order may no longer work as the father has moved away, or the other parent may not be collecting the child when he is supposed to. If circumstances change you can apply to the court to “vary” the order. The same procedure applies to this application, so you will need to follow the procedure set out above.

http://rightsofwomen.org.uk/get-information/family-law/child...