Addon not overwriting gui file?

Hello, I tried to make an addon to replace a file in garrysmod content.gcf, the file is in “garrysmod/materials/gmod/” as “recording.png”
So I made an addon like this “<addonname>/materials/gmod/recording.png” with the edited version, but nothing happened. When I start the game the addon is loaded correctly (loading legacy addon, etc) but when I start recording a demo it uses the png from the GCF… what am I doing wrong?
Also, the image I’m using is this: (uploaded to imgur)

I also tried just putting it in garrysmod/garrysmod/materials/gmod/recording.png but that did nothing. I’d like to get this to work, and if it does I would upload it to workshop because all my friends hate it too.

P.S. Sorry if I put this in the wrong section but this doesn’t belong in LUA coding obviously as it has nothing to do with LUA, it doesn’t belong in Gamemodes because it has nothing to do with Gamemodes, it’s not General Discussion, etc.