You can make a style hack also.
Open the theme .mssytyle with WSB go to Start Menu > Panels > Aero > Top
right click one image at a time first one and export all properties and do that for all the images
then after you do the last one right click again and export for all properties to a style hack
give the style hack a name and description and click create
then load the other theme and go to the style hack button
and find your hack and apply it