I'm not doing that at runtime, I need to do it whilst animating a character in Spine. For example, making a character turn around in an animation sequence.
Usually what I do in such cases now, I create TSR keyframes for every bone and controller in a frame, and then create TSR keyframes for every bone and controller in the next, but with -1 scale. I change the former keyframes interpolation to stepped. And then there's loads of work of making it look like turning around 🙂
However, I did come up with an easier way to go about it! I duplicate the attached images, and set their local scale to -1. Then they have to be moved and rotated into place. When I need to flip the character's body parts, I just activate the duplicate image. Might be a good, practical solution.