There is a program for the Pocket PC called Pocket Blinds. I seem to recall some folks trying skinning the H/PC desktop with that, but I don't recall the outcome. As for changing icons in Windows CE, you
can change the icon embedded in a Windows CE application using a resource editor on the PC. There are even a few on-device resource editors for Windows CE, though the ones I've found I haven't been able to figure out how to use.