you will be able to target terraforming with the next major patch. Even hostile terraforming. When you select a terraforming ritual, the popup will not only give you the options yes and no, but also "select target first". in this case you can select a plot on the worldmap and the Ritual will be done. For hostile terraforming the plot must be revealed so that you can select it. The disadvantage of selecting targets is that it usually effects less plots than the non targeted one. A few rituals like create land must be targeted.