how to switch to pose mode.
Make sure you have the rig selected and press Ctrl + Tab (in 2.79)
Or just Tab and chose Pose mode (in 2.8)
You can also change the mode in the header/footer
In blender > 2.82:
1. Select the object (In object Mode)
2. Press F3 (to open the search bar)
3. Search "Make Library Override"
4. Select "MultiBall_rig"
