xtctl is a script for setting/changing xterm properties. It can change the foreground, background, cursor, and mouse colours of an XTerm window, and the icon and background image (only known to work with Eterm). xtctl can also modify the window's title, icon name, highlight background, font, size, position, z-order (raise and lower), and iconified/restored status. There are experimental options for full and soft reset.
Xterm controller wars! :-)
It just occurred to me that others might be interested to know that I got all of the control sequences used by xtctl from ctlseqs.ms in the Xterm sources.
See the "get" functions in xtctl for an example of something that really makes more sense to implement in C (but I could hardly admit that at the time, could I).
See also xtctl (http://freshmeat.net/projects/xtctl/), which is a simple Bourne shell script that does this plus a whole lot more.