Note, that a rotation of 180 on the Z axis will make the image go upside down. This is not the same as a rotation of 180 on the Y axis, as that will make the image flipped left to right. If that is what you actually want (it's what your original post asks for), you can rotate 180 on the Y axis, but you need to enable the "double sided" checkbox on the material that you have on the quad, otherwise the reverse side of the material will be unlit/black.
#XPression