For now i know it's something related to ESD/Flags and i have to add the option in Andre to be able to reinforce armors.
#How do i make armors sets reinforceable?
foggy carbon
lapis hedge
I think you can add a shop like thing that gives you a armor piece at cost of an old one + something else or you could integrate the armor into the weapon upgrade thing with just making it reinforceable but then you would have to add a speffect in emevd that adds resistance to the different damage types when the armor piece is equipped. Thats how i would do it in elden ring (i dont have ds3 modding experience) but it should work for ds3 aswell