seamless coop and carrian warriors works together already so long as you use mod loader and mod engine 2. this is a patch for those that found it way too easy and want to use the harder coop for seamless mod. this is a modified regulation.bin file that patches carrian combo warriors into the harder coop mod.

how to install:
install mod loader(read description on its mod page for clarification)
install mod engine
install seamless coop into your steam.../eldenring/game/mods folder you got from modloader.
install carrian into your modengine mod folder
install this and replace regulation.bin in your mod engine 2 mod folder

how to update:
update seamless coop into your steam.../eldenring/game/mods folder you got from modloader.
update carrian into your modengine mod folder
install this and replace regulation.bin in your mod engine 2 mod folder

for reference i recommend using dsmapstudio to patch your game and here is a link on how to do it.

https://www.nexusmods.com/eldenring/articles/174

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there is a new mod that continues this mod for the newest version 1.09.1. here is the link. I havent tried it myself yet unfortunately if its not fully working or anything let me know and ill see if i can whip up a new patch on this page
https://www.nexusmods.com/eldenring/mods/3474?tab=files