I have a Mac running Snow Leopard (the latest) and UM Home. When I select the 1440x900 skin and quit the program, the default skin loads the next time UM is launched. I had run a trial of Pro UM and the selected skin stayed selected, so I believe it always should, on all versions. I even tried deleting the default skin but it loaded the next time I launched UM Home.
I tried downloading the 1440x900 skin again and it still does not stay selected in UM Home like it did in UM professional. I also noticed when I adjust the “knobs” for monitor volume and others, the new image does not line up with the unmodified image.