Oh, you don't need to follow that guide if you're using the intel plugin - the tutorial was moreso for the nvidia plugin, which has those issues.
The intel plugin does have it's own quirk when reading colour channels of normal maps, though - and that is that it blacks out the blue channel, which causes the normal map to look green. This can be fixed by inversing the blue channel. But honestly, considering that you already need to invert the red and green channel for your mesh, I would probably just invert the whole image in one go in this case, rather than doing each channel individually.
I don't think the mod maker is all too fussy about the normal map format having to be saved with ATI2N - it does allow you to import DXT5/BC3 compressed images as you noted, and it doesn't seem to make much of a difference. So I wouldn't worry about that part.
Last bit I would mention is to remember to generate mip-maps if you do not want your mesh to have a sort of fuzzy effect when zooming out, not generating mip-maps on the normal map can do that.
Edited by Dmitrias, 09 March 2022 - 06:52 PM.