For textures you can use
SetTexCoord to change the orientation of the image inside the texture region.
For a full size image, normal orientation is (0, 1, 0, 1). To flip horizontally change to (1, 0, 0, 1) and to flip vertically use (0, 1, 1, 0).
As for just flipping a frame, region or fontstring etc., I don't believe you can If so it would be lists
here.