What happens after the divorce is final? Well, nothing... until a party files a Motion to Modify Final Decree. What's happening here is that a party to the divorce is asking the Court to change the terms of their divorce decree. Here are a couple of the more common things that could be changed.
To change child support you're mostly going to need to show a significant change of income. This isn't all that hard to do, though keep in mind that if you're wanting to lower your child support payment you're going to have to show that your decline in income isn't your fault. If, for instance, you quit your job or voluntarily took a new job with lower pay or did something stupid to get yourself fired, then you're much more likely to be stuck with your child support payment. If you got laid off because of economic conditions and are diligently looking for a new job, then your situation may be somewhat better.
To change child custody you're going to need to meet the Gibbons test, that is,
"(a) that, since the making of the order sought to be modified, there has been a permanent, substantial and material change of conditions which directly affect the best interests of the minor child, and
(b) that, as a result of such change in conditions, the minor child would be substantially better off, with respect to its temporal and its mental and moral welfare, if the requested change in custody be ordered." Gibbons v. Gibbons, 1968 OK 77.
In practice, it proves very difficult to meet the Gibbons standard.