No,

You don't have to drain the coolant to change the switch on the thermostat housing, though be ready to catch it as it comes out. If your quick about it you should lose only a small amount (half gallon) that you can replace with water. The other switch on top of the engine, doesn't have this problem. The new temp switches don't come with new washers. I would suggest first taking off the temp switch thats on the top of the engine and using it's washer on the new switch for the thermostat housing so when you take the old one off you don't have to play around switching washers while all the coolant leaks out. Take the washer from the old switch you took off the thermostat housing and put it on the other new switch and install it. I think that pretty much covers it.

Chris