How to migrate the format of a unique non nullable flask model property?

Question

I would like to change the format of a model property and its name. The property must be unique and not nullable.

It is unclear to me as to how I would go about making the migration for this stuation.

Model before migration:

class MyModel(db.Model):
        hexdata = db.Column(db.String, nullable=False, unique=True)

Model after migration:

class MyModel(db.Model):
        base64data = db.Column(db.String, nullable=False, unique=True)