So this is either embarassing or not possible. For the past hour I'm trying to set tile yields in the editor. The best option seems to be tile modifiers in the objects menu. However that only leaves a purple square with the label mod on it and doesn't show anything in game. Am I doing something wrong or is it simply not possible? The latter seems improbable, somehow you have to be able to do it in order to create maps from scratch but I can't figure it out for the life of me.