Why do all shaders become diffuse after reimporting a model?

Hi, everyone! I'm making a model of a building and constantly overwright the fbx file I'm working with in the project folder. But when I do it previously set materials(I use reflective bumped specular) switch to plain diffuse shaders and I have to reassign them again then I update the fbx again and again all the shaders become diffuse. Can anything be done about it? Can I, for example, set reflective bumped specular as the default shader? Or I just have to finish modelling and after that set the shaders I want?