I need to override some basic fucntion on my server before all scripts will be run (gamemode, addons, …)
You’re better off not doing this and instead doing it the proper way.
What’s that? You’re still here? Well then, to have your Lua file be ran first, add an include for it at the top of garrysmod/lua/includes/init.lua. You’ll have to redo this every Garrys Mod update.
Remember that this is where all the libraries and modules are ran, so be aware of when you load your files.