Change the direction of the Gradient Wipe Transition

Exactly how I would do it but if I may expand on one thing.

To have the images flipped/facing  the original way in the end you can first flip each image
180 on the Y axis so they are opposite of the way you want them.

Then apply the steps to flip the gradient swipe.
Add the Page Flip effect, Group it all, Rotate the group 180 on the Y axis.

The images should be facing the original way when played back.

Should be no need to flip the images in another program first.

:)

This worked for me too - I wanted the radial wipe to begin at -45 rather than 0. So I made sure the image was turned 45 degrees before I applied the transition, grouped the two images, and rotated the group back to 0. And it worked! Thank you for this workaround.

PS: I discovered another tip. If you want the transition to act as an APPEAR - not switching between images, but introducing an image by itself - you can do it this way:

1. Create a dummy image using a plain box. Place it before the image you want to introduce.
2. Set up your image as you need it to be (e.g, I rotated mine -45 degrees).
3. Follow the steps to adjust positioning as above.
5. Once you're satisfied, DELETE the dummy image.

You're left with a group consisting of one image. All the work you did still applies, and your timing won't be messed up.