If that doesn't change your client art, then it's possible a virtual art file is overriding your actual art file. In the client directory, look for a button at the top that says "Compatibility Files". This will take you to:
C:\Users\Username\AppData\Local\VirtualStore\Program Files\Electronic Arts\Ultima Online Classic
If you have another artLegacyMUL.uop file in there, delete or rename it.
If you cannot find a virtual art file, but the tree hack still isn't working, try running Razor/UOSteam as administrator. Make sure the "data directory" settings in Razor/UOSteam are not pointing to different art files.