A parent scene file can be adversely affected by edits that are made at the referenced child scene file level of the hierarchy. The following section provides some examples of edits that can affect the parent scene’s ability to resolve previously made edits:
Do not change the DAG node hierarchy of a referenced file. If modifications are made to a DAG hierarchy in a referenced child scene after it has been referenced into a parent scene, such that the DAG paths change from what the parent scene’s edits specify, the edits may no longer be possible, or may be applied in a fashion that was unexpected.
If you rename a node in a referenced child file after it has been referenced into a parent scene, any edits that were made to that node in the parent scene will no longer be possible. For example, two nodes exist separately in a referenced child file, and have an edit that connects them in the parent scene. If either of the nodes are subsequently renamed at the child file level, the parent scene will be unable to apply its edits, because of the name change, and display an error message.
A keyframe on an attribute connects the attribute being keyframed to a new node. If the parent scene file cannot find the node (because its name has been changed), the animation may break.
It is common to add, delete, and rename attributes in a character rig. Creating a specific character node can work as a safeguard for any successive changes. Create the character node in the rig file that will be referenced rather than in the parent scene file that references the rig.
When referencing character sets, renaming a member of that set or renaming the character itself is not permitted if the referenced file modifies or connects to the renamed object. This could result in the animation not affecting the character set or affecting the wrong member of the character set.
As of Maya 2014, the Character Set automatically determines the offset objects (or roots) of a character. If the offset object is outside the DAG hierarchy but connected to it, Maya does not identify it as a root to your character.
In situations where the surface geometry in a referenced file must be edited, the user can add history to the referenced model. An example of this is pre-lighting when an effect used to store the shading and lighting information from the rendered look of a mesh in its vertex colors. As long as the poly geometry in the referenced file has history, new history can be added in the parent scene. A simple way to add history in the reference child scene file is to select the mesh and then select Edit Mesh > Transform.
If you change the value of an attribute in a referenced child scene file, there is no way, other than an immediate Undo, to set the attribute back. If it is important to return to that value, consider storing that value by setting a keyframe, Trax pose, or Trax clip. Another option is to store the value as a node preset in the Attribute Editor.
When you create file references with the group option, some objects in the hierarchy may receive a double transformation when the new group node is translated, rotated, or scaled when working in the parent scene. For example, when you translate an object, the object receives two commands to transform based on its location in the hierarchy. This can readily occur with rigged characters where a relationship already exists between the skeleton and the skinned character. In these situations, you must either turn off the Inherit Transforms attribute for the item in the referenced file, or determine an alternate approach to grouping the hierarchy.
When multiple users are working on a project, and one user is editing a referenced file that is also referenced by other users, the other users will not see the modifications made by the first user in their own parent scene until they reload the file reference. See Reference Editor.
If you require nodes to be written out as part of the save reference edits operation, you can import the referenced file so all of the items reside in the scene, and then select only those imported items, and export the selection as a reference again. In this way, all of the edits to the nodes and attributes will get written to the exported file reference.