So here is a few observations:

I had a 6 flight itinerary booked to Miami from DUB for this summer and I couldnt get the leave from work so I called them within 24 hours and changed the dates, Added 2 extra flights and also changed the destination to Hawaii all for free within the 24 hour period, I then found better flights and called them up again with the same 24 hours and then they let me change it again to that again with no charge as within 24 hours.

I did it this way as I didnt have enough cash to pay twice so got first one edited twice and also paid the difference. Was no hassle either way.

One thing to note is that you can pay a £10 fee on the web to hold flights and prices until you get approval but you lose £10 if you then dont go ahead with it, Might be an option for the future,

The above was just my experience with this and is no means the "rules" so to speak