Replacing Assets and Resources - Ryhon0/VostokMods GitHub Wiki

Assets can be replaced by placing a file at the same path relative to res:// and your mod's folder, e.g. to replace res://foo/bar.png, you need a folder named foo in your mod's folder with a file named bar.png inside it.
However, this won't work for most files as they have a .remap or .import file and need to be in a format digestible by the engine. Godot checks them first when trying to access a file, but it can be overriden by your mod.

The recommended way of doing this is by using ModZipExporter