irr::video::SMaterial * mat = sky_node->getMaterial(0);

///change mat type and any settings you need
mat->MaterialType = YourMaterialType;

mat->setTexture(0, mgr->getVideoDriver()->getTexture(
                getTexturePath("glow.png").c_str()));

mat->setTexture(1, mgr->getVideoDriver()->getTexture(
                getTexturePath("sky.png").c_str()));
                
mat->setTexture(2, mgr->getVideoDriver()->getTexture(
                getTexturePath("moon.png").c_str()));

mat->setTexture(3, mgr->getVideoDriver()->getTexture(
                getTexturePath("stars.png").c_str()));