Is that specular lighting that needs to be changed the model material not that model creation ? I'm not sure.
ent_mtlset (my, mtl_shaded ,1);
or maybe
MATERIAL* mtl_sdark ={ ambient_blue = 0; ambient_green = 0; ambient_red = 0; diffuse_blue = 10; diffuse_green = 10; diffuse_red = 10; specular_blue = 0; specular_green = 0; specular_red = 0; power = 0;}
ent_mtlset (my, mtl_sdark ,1);
EDIT Final