I tried figuring it out myself, but starting from scratch I am still struggling. It seems there are a lot of changes need to be made. For now what I am guessing is that animations and skeletons need to be unpacked, and existing ones in vanilla/Kingdoms replaced with the ones from SS; then packed again. Idk if descr_skeletons needs editing, Kingdoms file has things that SS is missing, and SS replaced some things that vanilla and Kingdoms have. Also, in SS animations folder there are subfolders (before unpacking) that are also inside animations pack.dat (when unpacked) - they seem to be adding some stuff too, but they are not packed.
All in all - I am mighty confused, and need some direction. Please help.