More - Shabbot Clocks

Question

After reading through your responses to the shabbos clock issues - how far does the hetar of gruma exetend - for example if I have a shabbos clock plugged in on shabbat - an it's set to the off position can I change the device that's plugged in i.e unplug a lamp and plug in a fan to go on at a later time? This is assuming that a lamp or fan is not muktza.