Step No.2 : Also download the DDS file Extension Plugin and put it into C:\Program Files\Paint.NET\FileTypes
Step No.3 : Open up a map in HMT
Step No.4 : Look for the bitmaps tag
Step No.5 : Select something easy first such as the Banshee
Step No.6 : Save it in a folder and make a backup
Step No.7 : Open Paint.NET and open the DDS file
Step No.8 : Do whatever you want to it then click save DON'T DO ANYTHING AFTER THAT!
Instructions:

Step No.9 : Exit paint.net and click inject texture in HMT
Step No.10 : Then click update close HMT and test it in halo!!!
~Nawuto HAPPY MODDING!!!
PS : the skin there is my BLACK MED KIT Which is found here My best skin