How to remove specific parts from vertex morph

1. Right click the morph and select Vertex/UV Morph Edit.
2. From Morph Editor window, go to Edit > Collect Vertex - Difference. This will hide unchanged vertices.
3. Select the part you want to remove, then from Morph Editor, click Edit > Set Original Position. This will reset the selected vertices to their original position.
4. And finally, click Update to apply the edit.

credit: コロン式初音ミク v2.1