You can change the appearance of an object by selecting a different image in the editor with a patch installed that allows you to edit object properties, or in the standalone version of the WoG editor, which already has the patch built-in: see the topic http://wforum.heroes35.net/showthread.php?tid=1517
By the way, just between us: there is a topic here called "All questions about Mapmaking" /topic/5758/
In the future, please ask your questions there: they will definitely be seen and answered! :)
(Василь Симоненко. Люди – прекрасні)