Yea it's called world edit, theres a ton of commands that help you with building. Remember that triangle of beacons wally created? That was world edit as well.So you just build half, input a code and it builds the other half for you?
Pff you don't even have to be ingame for terraforming these days.you can also clone, change block, cut part of built and another tons of other usefull stuff while building ^^
Terraforming also suddently become easier with commands ^^