Help me to link new texture dds and gr2 file

[oxygene2438]

hi everyone!
I created a weapon with 3d max and texture.
I'd like to replace a GM weapon by my new weapon (just to rename the gr2 and delete the old gr2 file)

My problem is that I want to implement the new texture without me use other dds files (weapon_choegogeup etc ...)
I want to add a new file dds

What is the link between dds and gr2?

Sorry for my English (I'm French)