You can make an action run within another action, thus reducing action complexity. For example, you could create an action that performs a dozen or more commands (it's not unusual), or you could create two simpler actions, and have one action load and run the other action. That way, when it comes time to modify the action, you have a smaller list of commands to deal with. You can also call actions from more than one source, giving you the ability to create small action codes that can be used over and over again.
Actions palette.
expand triangle of the action you want to modify.
Record button.
Play button to record the second action into the first action.
Stop button.
The second action is recorded inside the first action.
IMPORTANT
When you click the Play button, the action executes on the active document, so you might want to perform this on a duplicate image.