I'm not entirely sure whether I should leave the topic altogether and concentrate on GSE instead?
Because in my original version of this mod, it was not possible for me to add really new skins, but only overwritten existing ones. I noticed this when I wanted to integrate a total of three more. These then either overwritten existing skins or were simply not selectable and the engine ignore it.
In addition, SH5 has this annoying bug that the skins are not always displayed and SH5 loads the default skin. And if I only overwrite the standard skin with the graphics file, then all submarines of the same type will have it.