Mountains are Step Pyramids on a planet I made and I am unsure how or what would be tweaked to get a better slope on them. I have not found much info on terraforming and and basically trying to take either an Ocean type planet w/o seed from Purgatory or the default Ocean planet and add to scenario.
you use stamps in order to set the shapes of terrain. It works like it sounds; basically it 'stamps' the area of a biome with one of the predefined stamps in Content/Stamps. Note that the number corresponds to the planet size it would be compatible for (1 is smallest). Keep in mind stamps themselves can technically alter the biome that it's contained in, depending on your biome selectors. For example, making a huge mountain in a grasslands biome would probably have the top of the stamp have a low mountains/mountains biome.