When a file reference is created it appears loaded in the scene. You can use the Outliner Reference menu or the Reference Editor to unload references or reload previously loaded references.
See Loaded and unloaded references.
When you open scene files that have associated file references, you can specify which references get loaded. See Selectively open file references.
To unload or reload a reference from the Outliner
The reference is unloaded indicated by an icon.
The reference is now loaded indicated by an icon.
Unloaded referenced nodes are dimmed and the icon changes. If you unload a nested reference that has child references, the child references are also unloaded with the parent.
To unload or reload a reference from the Reference Editor
You can load or unload references based on the selection of one or more objects within the scene. To do this
You can specify which file references, if any, are loaded automatically when a scene file is opened. For example, you can select a reference and have it preloaded each time its parent scene opens. You can also set file reference options so that a scene opens with either none or all references loaded. For information about reference loading options when opening scene files, see Open Scene Options.
To specify which references to load when a scene opens
You scene opens with the selected references.
To specify that no references are loaded
To specify that all references are loaded