There is a very specific way of renaming a column, you must use the rename attribute for a field e.g.

name:
    type: varchar(128)
    rename: full_name

Once you run the migration, the field name will be changed to full_name, and any future migrations under the same file will resolve renamed columns to the rename column, ideally once you run the migration you shoud re-map your database or modify your schema files to correspond to the new format, and re-commit to your VCS.

WARNING!!

This allows you to rename a column without losing data, changing the field pointer itself will cause schematic to delete the previous column and just recreate it again, setting the rename will do a real column rename.