With your code I have adapted it to OPENWRT. In web interface Luci, in System->Scheduled Tasks copy:
*/3 * * * * uci set wireless.@wifi-iface[0].macaddr='40:53:50:4f:4f:'`/bin/cat /proc/interrupts | /usr/bin/md5sum | /usr/bin/cut -b 1``/bin/cat /proc/interrupts | /usr/bin/md5sum | /usr/bin/cut...