There is an old post by @Joanna on how to add your textures in PL2 - see How to add your own textures to DxO (FilmPack) [macOS] .
That was for Mac, on Windows look into the
“C:\Program Files\DxO\DxO FilmPack 7\Resources” directory.
The method probably requires some modifications to work in PL7, e.g. maybe you should also populate Textures\Previews. I was thinking of using some pixel editor but maybe one can still do it inside PL7?
It seems Textures/Framing/Defects were added just for fun, family photos, etc. PL is mainly a RAW developer. The rest should be done in graphics editor.