An administrator has just changed the IP address of an interface on an IOS device. What else must be done in order to apply those changes to the device?

nothing

Explanation:

the changes done on an IOS device take effect as soon as the command has been stated and the Enter key is pressed.

It is enough if "IP address" of an interface is changed and nothing else needs to be done. The reason is that, as soon as the command for the IP address is rightly typed, and then the user press the "enter key", changes take place automatically.

The same is the case for changes done in the router. As soon as the command for change is entered and then the enter key is pressed, changes will be implemented immediately. If suppose, the command entered makes system unstable then the device needs to be reloaded.