Help with .Obj export modification

I have no real experience with python so if someone more experienced could help me out. I’m exporting object from blender to use with blitz3D, more specific Gile[s] which I use for lighting and scene builder. Problem is that blender uses little bit different coordination system and object export in wrong orientation. How I rotate and possibly flip mesh in python script while exporting? (example would be nice)
I already modified .obj export that it just exports selected object.
Is there export format that I could export whole scene but still object as a childs to scene, so they are not one mesh…?