spy.py

#!/usr/bin/env python
import base64

import click
import oyaml as yaml


@click.command()
@click.option('--decode/--encode', default=True,
              help='base64 decode or encode')
@click.option('--out',
              help='write the output to this filename instead of stdout')
@click.argument('filename')
def spy(decode, out, filename):
    with open(filename) as f:
        data = yaml.load(f)
    secrets = data['data']
    for name, val in secrets.items():
        secrets[name] = (base64.b64decode if decode else base64.b64encode)(val)
    if out:
        with open(out, 'w') as f:
            yaml.dump(data, f, default_flow_style=False)
    else:
        click.echo(yaml.dump(data, default_flow_style=False))


if __name__ == '__main__':
    spy()

Before running spy.py, create a virtualenv, activate it, and pip install oyaml click.