Thank you a lot for the update, i tried it last night and that seems to work perfectly ^^ (at least, i have the correct backup options for Normals ^^).
I don't tried to use the converted textures yet into the game but i will send you a feedback if something go wrong.
About your 2nd reply, i think i said a non sense, i was in error because the exported files were not correctly opened with Paint.net but were correctly opened with the plugin, for BC1 and BC3... so I supposed the format has also been changed... but in fact, they are correctly read by the game if i use the "standard" compression format from paint.net. I have the feeling that they switch to use the sRGB format wich is also probably not managed by the default DDS plugin...
In another hand, on your side, have you got a batch processing plugin that can be used with this DDS plugin please ? (you will save my life one more time ^^).
Have a nice day ^^