Export, Import tool for *.apti_tex files. Plague Tale Games.
You can use the UI version or the Commandline Interface(WIP).
Open the app, then click export to export DDS from *.apti_tex files. You need to edit this DDS or at least make sure to convert it through GIMP "BC3/DXT5". Other compression support will add soon.
After your editing is done, you can use the Import button to import your DDS file to the *.apti_tex file. Simple enough.