If someone "pranked" someone by leaving a burning cross on their lawn, would the technicality to overrule any magistrates conviction be applicable too?
What "technicality" are you refering to?
Appeal courts, in Crown courts, can hear appeals against sentence and/or conviction from Magistrates courts in all circumstances.
There is a clear difference between sending someone an everyday object with a negative racial connotation in certain circumstances and leaving something burning on their front lawn!