After you get a divorce judgment, you might think that's the last you'll have to deal with any of those old issues. However, if you find out that your custody arrangements aren't going to work, that your ex-spouse had a change in circumstances or that you've had a significant change in circumstances, it may be time to ask for a modification.
Asking for a modification of your divorce decree isn't necessarily unusual, depending on the reasoning. Many parents ask for modifications to adjust child custody, for example. Others may ask for modifications of alimony when they're getting remarried or have a change in their circumstances.
When you seek a post-judgment modification, you're asking the court to modify the final judgment previously made. For instance, if you have a child custody arrangement in place that doesn't work any longer, you may ask the court to modify that arrangement. If you have a property division settlement agreement that you want to have altered, you can ask for that as well.