As the title suggests, this suggestion is to be able to 'paint' terrain with mire in the editor, rather than having to have all the land being mired normally. This would generally be helpful for miring larger portions of land that take a long time to be mired normally, or would become insanely laggy whilst it's being mired (as well as giving some control over how much of the land is initially mired). This idea cropped up when I discovered how much performance is eaten up by enemy Mire Spawners, during my attempt to make a map based on a "planet surface".