Why don't you try my ba-GUI-nnertool ?I'm pretty noob wth that stuff so, could you give me a direction to look on what to do to edit my .cia and make them have your banners ? Tried to open them with 3DSexplorer to start, gave me a ticket error...
https://gbatemp.net/threads/release-create-2d-3d-banner-smdh-with-ba-gui-nnertool.406433/