At some point in the indeterminate future (that is, it’s far too early for Radiant to give any release dates), there’s a planned class known as the Geomancer who should be able to help with this situation. Effectively they would be a “reverse miner”, able to create terrain blocks.
One thing I’d really love to see is a way to spread grass onto normal dirt, but only by choice. Having Minecraft-style grass spread would be nice, but I suspect that a lot of us would get frustrated by grass spreading into places we didn’t want it. Of course we can build wooden roads which look like dirt; but that seems like a pointless extra step. It makes more sense, IMO, to have some kind of job for enriching barren dirt with some kind of fertiliser and then sowing the seeds for grass to grow and spread. Of course, the benefit of doing it that way is it also allows us to create grass where none was before.
I would think that such a job could be carried out by any worker; but creating the fertiliser/grass growth tonic should be a task for the Herbalist.
In the meantime though, you may find [this mod] ([Mod] Slabs with terrain colors [A20+]) very useful – it allows you to place down slabs or floor sections (and even roads, I guess) which have exactly the same colours as the natural terrain. I presume they won’t work like dirt/grass for farming on, but for filling up the goblin camp hole and so on, they should be mighty useful. Plus, add some gold decoration or green roof sections to your constructions!
Regarding the other half of this suggestion: it would be awesome to be able to merge buildings into a single floorplan after construction; allowing us to easily extend buildings with a new structure and then merge that into the original floorplan. I’d further like to be able to add extra windows and doors at a later stage, so that as the town grows around the building new access can be opened up on all sides. Moving previously placed doors and windows might be too much hassle to implement; but simply punching out a hole for a new one shouldn’t be too hard by comparison.
I hope that all these sorts of things get added as the game progresses – at the moment Radiant are dealing with critical fixes, but it’s the seemingly small features like this which make a great game cross over into the real of legendary classics.