Pretty much every field that can be edited in iTunes' Get Info panel can be updated in mp3tag. I haven't used the iTunes editor for a long time due to many limitations there, including the poor filtering. But that is why we have mp3tag! Do note that any changes made outside of iTunes will require you to force a library update. See here for some guidance.
An example of a video file I have, including the DESCRIPTION field you mentioned, that is similar to the podcast tags;