A simple scripts that turns 'Ctrl' into 'Super' key in X. It also reverts the changes made by your desktop environment by monitoring xkbmap periodically.

gistfile1.sh

#/bin/bash

# 0 - Init, 1 - Set XKBMAP
KBD_STATUS=0

while true; do
  KBD_OPT='caps:super,terminate:ctrl_alt_bksp'
  if [[ $KBD_STATUS -eq 1 ]]; then
    setxkbmap -query | grep -qF "$KBD_OPT" || ((KBD_STATUS=0))
  fi
  if [[ $KBD_STATUS -ne 1 ]]; then
    setxkbmap -option
    setxkbmap -option "$KBD_OPT"
    ((KBD_STATUS=1))
  fi
  sleep 5
done