Question re changing parenting orders

I have a question posed by a friend that I thought some of you knowledgable ladies might be able to help me with.

My friend and her XH have shared custody of her two primary-school aged boys. This has been put in place with a court-ordered arrangement. Neither party is particularly amicable to the other, unfortunately.

Long and short of it is, after a change in XH's situation (new full-time job involving interstate travel), it's becoming difficult for him to fulfil his share of the custody arrangement, without needing her to be available to take the boys if he wants to go away at short notice.

If they both would like to change the current custody arrangement, do they both have to go back to their lawyers and redo the whole thing? Or is there a simpler way to change the arrangement if they both agree with what they'd like to do?

If they both agree to the change in custody, then they can apply to change the existing court order by going through the same process they would if they were applying for the first time. They would have to sign draft consent order and then the Family Court can make it into orders without them having to actually go to court. It sounds nice and simple, but the forms may be complex, so for peace of mind she might want to have a legal representative do them for her. This way is only going to work if they can both agree on the terms though, which may be hard when you have two parents that aren't on great terms with each other.

My DH and his Ex originally had their custody arrangement done "properly". I don't think they went to court, but it was all done documented through the child support agency. Since then it's been changed a number of times (if fact, my two DSS's now primary live with us and not her) and it's never had to be changed "officially" (although DH and the ex both have a signed copy of some paperwork that they had notorised stating the changes). The amount of child support we pay (yes, can you believe WE are the ones that still have to pay out the child support?!) is just worked out from the child support calculator online to make sure that all is done "above board". We also used to keep track of exactly what time the boys spent with us just in case their Mum tried to pull anything dodgy on us. That way we had documentation as to how much they were with us. Having family members and friends to corroborate the time spent here would have also been easy for us. We've been lucky-ish in that the ex has never done anything super bad in regards to all this. The worst part was when the boys lived primarily with her, we were paying her heaps in child support (more than we needed to) and then she would ask us to go "halvies" in the cost of things like new shoes, school camps etc. Ummm, that's what the child support if for!

Thanks mylitta for your feedback. Interestingly, child support is part of the bone of contention here (she pays it, he opted to study full time and be a SAHD when he had the boys, so it became her responsibility to support him through it). Now he's gone back to work, he's not happy about that reduction.