UV Mapper is the tool many people use to tell an object where to look on an image to get the texture for each face of the mesh: you could (in pronciple) remap the Mil Horse to look in the same places as the P4 Horse, but it would be hard work and possibly limited i usefulness. Using Photoshop you could, with the clone, transform and liquify tools, push the P$ horse maps to fit the Mil Horse templates, but the quality would suffer in the process. Either approach would be a lot of work (though remapping would need to be done only once, and could be shared).