Is it possible to change the face that represents each person on Photos.app on OS X 10.10? I'd like to change the thumbnail selected by Photo.app for some of the people on the Faces album, but I can't seem to find that option. Also, consolidating some of the suggested names –which I suppose are contacts in some of the cases– would be great.
Right-click on the Faces album you'd like modify, and click Get Info. 
Double click the small round photo that appears on the fifth row of the info pop-up. All photos in that album will now appear behind this pop-up.
Right-click the photo you that you want to use as that Faces album thumbnail, and click Make Key Photo.