Currently you can import heightmaps for world tile resolution, but you can't go as fine-grained as embark tile or in-fortress tile resolution.
Obviously world tile is easier, since DF already supports that natively via its world painter tool. But I figure maybe somebody has figured out a way to hack into the world gen process at the point where it determines embark tile height or after it has done its erosion to determine in-fortress tile height, to replace them with something else. Doing it at THAT poitn is preferable, because then we can just let the default game do its own thing with aquifers and soil layers and all that jazz without help, and without having to re-invent all those wheels.
If not that, is there a way to do this after embark? I know that the community knows SOMETHING about tile editing, since dfhack has scripts for things like replacing a vein with another material, etc. Could this be extended to reshaping the entire map according to custom external data? For example, shaping an environment in minecraft, and then I know enough about modding that game to be able to export to almost any binary format, and then translating it into a custom DF landscape?
I know some C++ and lua and java and various other things and can do the actual conversion scripts myself, IF somebody can provide some help with understanding the "API" (unofficial) hooks that dfhack is using, or the means by which world gen might be accessible already. Just need a leg up. Unless a finished product method of doing this already exists.