Changing the engine oil while it is hot is the usual way of changing engine oil. It allows the oil to flow from the engine more easily taking less time.
Other then time-taken it will make no difference to an oil change.
Both the sump and sump plug will have the same degree of expansion, minimal, and will have no real tendancy to cause damage.
Damaged sump plugs are usually down to over tightening when refitting them, or ill-fitting tools when removing them.
Changing spark plugs on an engine with an alloy head is best done cold because of a difference in expansion of the alloy head and the steel body of the spark plug.
There have been cases of spark plugs snapping off at their hexagon on the plug body. This is usually down to the length of time new spark plugs now spend fitted in the engine, and over tightening when fitting. (How many mechs have you seen walking around with a spark plug torque wrench in their back pocket.)