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Click the checkbox to accept the changes.
This might be all you need to do - save the normal file as a PNG by right clicking on it.
You can also edit the intensity (usually the main thing to do) and the other options. Listing these on the creature model pages may be recommended to recreate it later (eg; if you change the texture size, or swap the texture).
For the specular you can use this to generate a good enough general spec map to later edit in GIMP or similar to change to NWN specifics. See Merrickdad's tutorial for most of this.
Specular and Roughness
These maps provide a shine to the object.
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