Is it possible to export animations/actions separately from Blender to Unity I want to have a 'master rig' file in Unity that I can plug a separate animation into. So then I can go and edit a single animation without having to re-import the whole FBX with the rig, mesh, and animation. 

The problem is that I have no idea how to export the FBX with just animation.

The single file FBX with all my actions works, it just annoying to have to rearrange the rotation, scale, and layers each time I replace the file.

Thanks in advance
If you're exporting to FBX manually from Blender, the checkbox Baked Animation will save the animation to the file. Keep in mind that you do have to select the Armature object type to export (and exclude everything else). The animations reference the armature for keyframes.
Alternatively, you can do this via Python script with the command:
bpy.ops.export_scene.fbx(... use_anim=True, ....)
I actually just published a blog post about exporting multiple FBX files for the purposes of importing into Unity. It's only Part 1, but I should have Part 2 written up sometime soon!
http://undertheweathersoftware.com/building-character-customization-part-1