Are there any way to stop Unity from upgrading a shader?

Question

A projector shader using the _Projector attribute will be changed to use unity_Projector, instead, in Unity 5.5. I'm writing an editor plugin that works on multiple versions of Unity. Such upgrading will make the shader not work in earlier version of Unity.

Is there any way to stop such upgrading?

Answer 1

You can prevent Unity from upgrading a shader by adding UNITY_SHADER_NO_UPGRADE somewhere in the shader, like in a comment at the top of the file. This was added in Unity 5.4.