Why do you need to make a trigger if you have OBJECT EDITOR? if you remove the Return Gold & Lumber Ability just for the distance of the building then what's the point of having a Town Hall?
here's a useful one, go to the object editor, click the town hall you want to reduce distance and find the "Pathing - Pathing Map", there you can adjust the path of every building you want as shown in the screen shot:
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it will end up changing the path into this:
View attachment 118397