Can you use the paint brush tool to directly sculpt the landscape like Terragen classic? For the most part the random landscapes work for me, but I have some slight alterations I'd like sculpt by hand.
You can, if you feed the painted shader into a displacement shader or use it as a blender for a power fractal or surface layer with displacement. But painting precisely is difficult, and be sure to make the preview window large enough to see what you're doing and most importantly... pause it! Or you'll likely crash.
Don't use the erase function too much, then you better start again with a fresh painted shader.
save often when using the painted shader, or also save different iterations of your tgd when using it.