thank you Kamal!
I was looking for something similar to what Paintshop has, I think you call it replacement tool. You can either replace a color, like the Swapper does, or you can put texture A on your brush and *only* where you come across texture B will it replace with the new A texture.
But I don't see that this exists in there, but, I was playing around with selecting a texture from the "textures used in this grid" list, while you have a grid square highlighted, and then playing with this I can kind of do what I wanted.
Wish I'd seen that tutorial earlier... I think I had to learn all that the hard way!
Like you say, the keys to good looking maps is blending textures and getting a feel for how the pressure works, and finally how applying color over all of that works.
Also avoiding flat ground, and big areas of repetitive texture.
And unlike NWN 1 you need to plan a map out mentally first.
I used to look at real life photos and try to duplicate them, but they never looked as good as a picture. It was more achievable (i.e. satisfying) for me to take screen shots out of Skyrim and try to reproduce those. Made for good practice.
One thing I also practice is draw a box / trigger and practice transitioning a texture from 100% at one end of the box, and fade to 1% at the other end, and have that texture transition look as seamless as possible.