The first hearing for the C79 will be a
directions. The ex will either accept as fact the
breaches of the order or not. If not, then the judge is likely to ask
parties to submit statements at which point you could add your additional
matterial.
If the final order is less than 12 months old you
could use a C2 to vary the order, if over 12 months as you say the
C100.
A judge might be prepared to change the order at the enforcement hearing,
but there is no certainty especially if you seeking substantial changes.
Best bet would be to submit the C2/100 and ask the clerk for the matter to
be listed alongside the enforcement proceedings.