Changes to the model schema can be made via the User Interface or via modules using Python. Which method are you using? You also mention migration. Are you migrating between versions? Perhaps some lower level detail about what you are doing and what's not working would help get your question answered?

Hi Ray, the question was not well posed because I didn't yet read enough docs to formulate it appropriately. In the meantime I read some docs, and understand I can prototype models and use them as templates for new models, which partially answers my question. But, what should I do if I want to modify an existing model, already in postgres and with table containing data? Hope now it makes sense. Thanks.