Hey there,
Yes-ish. But it is not a simple process. The base statement is that you can’t combine anim instances. However, when defining your skeletal mesh in mutable customizable objects, you can add animation instance metadata to the node. When the customizable object is compiled and built, you can query that metadata and determine what you want to do with it.
https://github.com/anticto/Mutable-Documentation/wiki/Node-Skeletal-Mesh
Post-process blueprints are more complex in this case because they are tied to the mesh, so you cannot use them as they are set up for those in particular. You would need to move those anim graphs out of the post-process approach and apply them as a linked layer approach.