I've tried it myself, and the sprites of course change in the game to whatever graphics you replace them with, but using the dimensions set for the initial sprite. I was hoping there would be a way to change the dimensions to match whatever the original image dimensions are.
Basically, I was hoping to make a skinnable game, which is possible without changing dimensions, but I could use being able to change those dimensions to match the actual image's dimensions at runtime, where those images may vary.
Oddly, I just realized a method by which this could be done in my case. I'll post that back here if I can throw together an example quickly enough.
Thanks for going through this one with me! Much appreciated! :)