I have interactive object where I change material, Lightmaps are build by gpu lightmass. So do I have to build lightmass for every material, because it doesn’t have logic to me, use same lightmass just different material? Everything is static for better hardware use (mobile VR, older cards etc). Or wayaround, use instanced material just change diffuse map inside that material and lightmap goes same?
you should google a technical brief of how lightmapping works. you can change materials without changing lightmaps. the static lightmaps nor the gi will update ofc.
light scenarios can do it to some degree, it seems. if you need more control you may have to resort to externally baked or simplified (white light) lightmaps, and come up with some controls and shader logic to tint the lightmaps. i see this very much working in a controlled environment.
yup I just change material everything work fine, not sure why I didn’t test it before I post on forum 
Now I need function in blueprint that just change diffuse