I would want to exchange this key with, for instance, the video shutter one.
Note that you can't just swap the shutter with another key, because the shutter is actually two keys: shoot_half and shoot_full_only in CHDK code.
If you assigned video to shoot_full, then when you click it the camera wouldn't wait for autofocus etc, and most shots will be bad. If you just want to CHDK scripts, it might be OK.
If you post which Canon firmware version you have, I can post a build with this change.