Yes you can create or remove anything at anytime in any script, however when you do create these items you have to take into account the amount and where you place them. But yes you can create movable items, fields, even entire maps.
If its just placement than you can randomize the placement while setting conditions not to set them in houses or pz zones. If removal is involved than you need to be specific about the placement, meaning you need to set exact coordinates or at the very least a scan of the area which can become complicated very quickly due to the stack order of things.