CodeX is a software similar to an application called CodeWalker, but it is eligible for use in modifying the RDR2 Map and much more. Additionally, it can be used in Fallout 4, GTA IV, The Elder Scrolls IV: Oblivion, and even Cyberpunk 2077.
I purchased CodeX for $1 but personally don't like the user interface (UI) and the application itself. I had planned to give it away anyway, so I have included the source code versions of both x19 and x20. If you wish to modify the application, you can do so, or you can simply get the beta release version. If you leakers want more RedM content, feel free to send me a direct message.