How to change nova db in Train ?

Buddies, I have a question about updating nova db. I would like to change the length of internal_access_path in console_auth_tokens, starting from Train. I want to modify nova/db/sqlalchemy/models.py and the migration file under nova/db/sqlalchemy/migrate_repo/versions. However I did not find a placeholder file for Train. 402_add_resources.py is the last one in Train and 403_ is "Add reserved schema migrations for Ussuri". So how can I do it in Train ? Yingji.