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- TXI (urg) can define it with EnvMapTexture
- MTR can supposedly use Texture15 for it, this needs further testing
- You can specify a texture filename in the appearance.2da entry (not a terrible idea, but only works for creatures not placeables or tiles)
Removing Baked In Specular Maps
Can use GIMP or in MindText2 you can use "Flatten Color" to remove the shine from a texture, from Defana:
It loses some of it's quality so it can be difficult to do properly.
Using Alpha as Specular
As noted above alpha layers are used for the environment mapping "shiny/reflective" surfaces. It'd be nice to get these converted over to PBR's though (which gives us some nicer control).
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