By default, Maya looks for the CharacterControlsConfig.xml and CustomRigControlsConfig.xml in the CharacterControls directory to open the Controls or Custom Rig tabs. When you load a new layout, the name and path of your customized file is stored as the new default that is loaded each time you start a new Maya session.
> Edit > Controls > Load UI Configuration
> Edit > Custom Rig > Load UI Configuration
The default is updated and your custom layout appears in the Character Controls. This layout continues to appear in the Character Controls window, even after you have ended your Maya session or open a new file.
> Edit > Controls > Update UI Configuration
> Edit > Custom Rig > Update UI Configuration
To load a new layout using MEL