A fifth idea:
Inject the vertex shader code into the render pipeline in general and use #ifdef statements to activate it. This idea is based on this post . The post mentions modifying Runtime\RenderPipeline\ShaderPass\VertMesh.hlsl, but as you can see by the path it’s not used exclusively by the Lit shader, which is where I think the #ifdef statements could be helpful. (Or maybe the person in the post forked the file and included it via #include statements) (Thanks for the idea @cubrman )