I seen terraforming in the context of extraterrestrial, but nothing really about small scale. Hopefully this is in an acceptable place, and not duplicating other work.
My land averages 7% slope, and has lots of small scale changes in curvature. The last time the land was worked, was when I worked it in grade 11 (I am now 59). So, it has been in mostly fescue pasture for a long time. It was a fescue pasture before I worked it up in 1976 or 1977, and had been for 30+ years (which goes back to WWII as to when that pasture might have been seeded). When I worked it up, there were not wild roses and aspen popping up all over; there is at the current time. So, it is feasible that the original pasture was seeded about the close of WWII. The land was homesteaded in the mid 1920's, so it has been in agriculture for slightly less than 100 years.
I am not planning to till any of the land. But there are places, where if I cut the top of a "hill" (convex area) slightly to fill a valley (concave area) nearby, it would make a following work of putting in a swale either uphill or downhill of the modified area a bit easier. My guess at this, is that you strip the sod off (on a cloudy day), and then adjust the soil profile where the sod has been removed. If you want the sod to be there, you then place the sod back on top. If you don't want the sod there, you cut the sod up and put it in the compost and seed to now exposed surface to something else (like white clover).
I did not seed the land after I worked it up. It was seeded to a mixture of fescue, clover and alfalfa. What clover, I don't know. I do know that there is alfalfa, white clover, red clover and some other clover(s) that people are calling alsike in the pasture now. I do not know if an innoculant was applied to the legume part of that mix.
I have some crimson clover seed, and I just bought some white clover seed. Normally, the seed places here want to sell you enough innoculant to seed all of the bag of seed (50 pounds) at one time. It is likely going to take me a year or two to use up 1 bag of seed. My soil is clay fr the most part, and I have some cleaned clay from a clay mine in southern Alberta. I could innoculate clover seed and make seed balls to throw on the landscape. Perhaps that is a way to (re)introduce innoculant?
More than 10 years ago, I tried to set up a raised bed garden in part of the pasture, and in the process dug down into the soil a big more than 1 foot. My recollection is that the soil was substantially the same throughout that depth.
I think this (and similar) jobs are a little big for a mattock (which I have), so I was planning to do this with a small tractor (when I get one, soon).
For me personally if I had a valley to fill I would look at putting a pond there, and connecting that to a series of swales. Check out videos and maps of Geoff Lawton's farm to see how ponds and swales are integrated into the land. This short video is also helpful: https://vimeo.com/168769052
From the NW corner of the house running slightly W of N, is a "north sloping ridge" in the lawn, which splits water (mostly spring runoff) to staying to the west, or moving east 150 feet or so. The water that stays west, just slightly downhill from our barn, heads NW and exits the property. Eventually I hope to adjust the drainage, to not have this water head NW. Part of the reason, is that this NW water runs past my sewage lagoon, and then runs past the neighbour's sewage lagoon as well. Which I don't think is optimal.
I did some ditching with the mattock last fall, which now has the water from the NW downspout running to the same place as the water from the NE downspout empties onto the hill of the lawn. About where the "lawn" ends, the slope flattens out to a shallow valley which in places runs NE or N. This part I want to "level" is part of this shallow valley. The valley may be 20 feet wide, so it is reasonably small. I was thinking of putting a couple of parallel C shaped swales on the lawn, which could have a pond where the land is currently lawn near the bottom of the C. I was hoping not to start that this year.
I did put in 4 tree swallow birdhouses, and I am in the process of putting in a bathouse on the south face of the barn. Which would work with swales and ponds. As both tree swallows and bats like taking mosquitoes out for lunch, so to speak.
I think someone said a picture is worth 999 words (or so). So, here's a picture (colours look horrible in GIMP).
The area in question is under black plastic (has been covered about 1 year now), and except where the deer poked holes in it where walking, I think the fescue is largely subdued. The triangular area between the board fence and the jackleg fence, has 3 raised beds in it.