The light probe shader uniform values are extracted from the material property block set on the renderer.
Property unity_SHAr, unity_SHAg, unity_SHAb, unity_SHBr, unity_SHBg, unity_SHBb and unity_SHC will be set to zero if they are not part of the MaterialPropertyBlock.
Property unity_ProbesOcclusion will be calculated as in normal lighting if it is not part of the MaterialPropertyBlock.
Note that using the light probe values baked at a different place may lead to incorrect rendering, especially when local lights (i.e. point lights and spot lights) are used. This mode is more useful when drawing instanced objects with Graphics.DrawMeshInstanced, where the light probe data is pre-calculated and provided as arrays.
Additional resources: MaterialPropertyBlock, MaterialPropertyBlock.CopySHCoefficientArraysFrom, MaterialPropertyBlock.CopyProbeOcclusionArrayFrom.