After rigging a charactor, you should group them for later use, by selecting only meshes, not the armature, and press ‘Ctrl+G’, the meshes will have green outline (instead of default orange). Then rename the group to a meaningful name from the object tab.
Start a new scene, you can link the charactor into this scene by ‘File’ -> ‘Link’ -> ‘Group’, make sure that ‘Link’ and ‘Instance Group’ is selected.
You’ll have 2 new objects in the outliner, the mesh and the rig.
If your 3D cursor is not at the origin, your mesh will appear off its originate position, you must reset it back by pressing ‘Alt+G’ to clear its location.
Then restrict the mesh‘s selection by toggle off its arrow in the outliner, so that you don’t accidentally move it out of place as you would only work with its armature in this scene.
You can enter pose mode and pose the rig anyway you like but you’ll notice that you cannot key any bone. You need to make a proxy of this amature to be able to add any key on it.
So, in 3D view while the rig is selected, press space bar and type in command ‘make proxy’ and click again to confirm. Now, you are able to key this rig.
Notice that the name of the rig would change into ‘_proxy’ and the link icon is disappeared. You can rename the rig to whatever you like.
Rigify rig comes with a handy script to toggle bone layers/ FK-IK switch from the right panel.
But when the charactor is linked into a new file, this script just got lost.
You need to ‘Append’ a text called ‘rig_ui.py’ from that source file and run it once to get the panel back.
append text from source file.
switch to ‘Text Editor’, load the appended ‘rig_ui.py’ and click ‘Run Script’ once.
Now the panel is back. while the ‘Register’ is ticked, the script will automatically run every time the scene is loaded, so you don’t have to do it manually again (for this scene).
Linking group is an efficient way to manage your project. You can link a charactor ‘group’ to animate him in the set before making small changes on polygon, UV, or many things later. And the changes will be carried over every scenes the charactor is linked.
You might, like me, keen on saving every version of source file, just in case anything goes wrong, and end up with many different versions of the same charactor.
before final render, with the master scenes linked to different source files, you’ll need to re-link them so that every scene links to the final one.
so, switch the outliner to ‘datablock’ view and find the ‘Libraries’. You’ll see ‘lib’ of every files that’s been linked into this scene.
Expand the ‘lib’ to find out which one’s which by its ‘File Path’
You can change the file name to the correct one. After saving and reloading the scene, it will be re-linked.