Grand Theft Auto 5 owners surely know about FiveM multiplayer modification framework, which allowed you to set all sorts of parameters on your server and tailor the experience to your liking. Now the team behind it released the same tool for Red Dead Redemption 2.
The dev wrote that RedM, which is what they called the Red Dead Redemption 2 edition of the tool, relies on CitizenFX framework and Cfx.re technology. It's obviously still fresh from the oven, so the documentation is a bit on the light side, but this should be amended soon enough.
If the features provided in RedM are any indicator, and they should be according to the dev, Red Dead Redemption 2 players should be able to customize just about everything. The network code is likely to be that of Red Dead Online with some anti-desync improvements.
"FiveM doesn't modify your GTA V installation, so you can switch between GTA:O and FiveM without getting banned", they wrote on FiveM's website, and the same rule should apply for RedM, i.e. you'll be free to switch from one to another without getting banned.
If RedM ends up anything like its older brother, Red Dead Online players will definitely have a difficult decision on their hands, because FiveM seems to be doing everything better than the official servers. You can find the comparison between it and GTA Online on this page, where they list all the advantages like maximum player count and no bans for no reason.
In related news, Rockstar recently rolled out a new Frontier Pursuit for Red Dead Online -, which lets players try their luck in the world of alcohol distilling and bootlegging.