mesh - How do you join two models together without messing up existing shapekeys? - Blender Stack Exchange
shape keys - Apply a modifier as a shapekey into existing shapekey or merge shapekeys? - Blender Stack Exchange
Non-destructive sculpting in Blender with Shape Keys – Victor Karp
GitHub - TiberiumFusion/BlenderShapeKeyTools: Split, merge, filter, blend, and apply modifiers to shape keys in Blender
Merging multiple OBJ files into one file with shape keys - Blender Stack Exchange
Pose Shape Keys Add-on: Rig Like Never Before! - Blog - Blender Studio -
GitHub - BlenderNewbie2020/Blender-Merge-With-Shapekeys: Small script for Blender 2.79 to merge two objects, adjusting the shape keys of the second (active) object.