In transitioning from deeps to mediums I have a deep and two mediums for brood chambers. So, if I find the top medium or both mediums full of honey can I take them off, treat for mites(lets say with formic) and then replace mediums and still harvest that honey for human consumption in spring if uneaten by the bees?
Yes, as long as the honey stores were not on the hive during treatment and a period of several days follows treatment before they are replaced. But why harvest? Invert the hive so the deep is on top, then in the spring if the deep still has stores harvest that and your transition is complete as the mediums are left as brood chambers.