When I look for a texture in a tileset I go through the following steps
1. Find the name of the tile in the toolset (lower left corner)
2. Open Nwnexplorer and search for the tile
3. Open the .mdl file and click on "Raw Model"
4. Figure out the bitmaps looking at the information you screenshotted above.
5. Open a new nwnexplorer and search for the texture
6. Export the dds (or TGA) to tga
7. Change the texture
8. Save it as TGA in the DDS converter "In" folder"
9. Run "Runme.bat" and fetch the new compressed dds texture in the "out" folder
10. Save the texture in a HAK above the old texture.
edit: Oh, this might not be what you asked for, but doh... i'll keep it here for someone else .)