redwdc's way will work, but then the modkey # will become out of sync. You don't need to edit the themevars.rc directly - all the options are available through the theme itself. But, it was kind of dumb of me to leave that hotkey as shift+x. >.<

The shift+x hotkey is to freeze xprop when making a color style, so you can "sample" colors (by right clicking the buttons in the style controls). To change the hotkey within the theme, hold shift and left click the desktop - select Style Options, then Style Controls. You'll see the "Current Hotkey" listed under the xprop viewer. To change it, click on "Set Hotkey." Click any modifier button (ctrl/alt/shift/none) and in the "Key:" box, put in what key you want to use. Then, click the check mark to the lower right of the hotkey options to confirm the new settings.