Wait if it's toggled only by a key what if there's a client that does not have the mod on that server?
sorry if this has already been addressed just making sure
You cannot see GUIs that you don't have. So that means you will need the Client-Sided part of this mod. Unless you want to type out millions of slash commands.
Can the person edit the code to make it for an RP/RPG that already exists?
They can, but why do you want it to be "built-in" with a rp mod?