Jack, another user posted a potential solution: https://umod.org/community/rust/22630-custom-item-icon?page=1#post-3
Note the different file path in his answer compared to the video.
Note the different file path in his answer compared to the video.
I know this is oretty old, but in case anyone else is tumbling across this, here is a very easy solution:
https://umod.org/plugins/general-item-modifier
just make a skin, enter the skinid and the shortname of the item in the plugin and your are good to go :D