I have had a quick, look at the agreement.
Firstly it clear says at paragrapn 1 on page 2 that
MMG may, after consultation with you make any changes to your job, titl, duties, location and reporting relationship as are reasonably necessary for the proper conduct of its business.
Also at page 4 under hours it says (Subject to change by MMG)
Further at page 6 under the heading hours of work the last sentence again says MMG will consult with you if your hours of work are required to change, however MMG retains the right to vary your rostered hours or shift roster from time to time
In both cases they have to consult they cannot impose it on you.
Having said this when you reached your agreement in the Family Court had you at anytime spoken with your employer and got any guarantees about your hours staying as they are. This is important.
If not then have they consulted with you and tried to find anything to allow you to keep working the hours and is everybody else in your area getting the same change?
They can change the hours the law lets them but they have to consult, and if possible work with you.
Have you looked at cases that have been decided under the sections you have raised?