How to patch (replace) a Roblox game script

I'm aware that exploit tools which use exploit API like WeAreDevs fundamentally have the ability to attach to the Roblox Player and inject and execute scripts into the game's runtime environment.  From there, an Roblox exploit can do many things.

However, what I want to do via an injected script is *replace* one of the game's script modules with my own version, thus altering the game's behavior itself.  But Roblox compiles the game's scripts as bytecode, and changing script.Source at runtime is thus of no effect, so really I have to replace the reference to this bytecode (which I don't know where it is).

So, trying to get some advice here on where Roblox stores the *reference* to the script bytecode so my injected script can change it to another injected script.  Was hoping one of the Exploit API's like WeAreDevs would be open source or have documentation, so I could see how the injection itself is done by the API and get some clues, but as this stuff is all underground activity, there isn't much support or assistance available except via the community at large, such as here.  

Any ideas on how an injected script could do what I want, basically change the game dynamically by re-writing some of its code?