New version of image converter works well all images.
And easier to edit MSE2 than MISE 1 files.
Export files with Monkey explorer to DDS, open with paint.Net, edit it and save new graphic with Paint.net to DDS (files with transparency use DXT5 ). And convert dds to dxt with Image Converter (MISE2 option). Put DXT file to proper directory.
(If you prefer Photoshop save DDS file in PSD format with Paint.net, edit psd with Photoshop, merge layers if finished it, save to psd. Open psd with Pant.net and save to dds.) (paint.net do not support psd with layer effects, so need to merge layers)