extend.py

import click

@click.command()
@click.option('--verbose', '-v', type=int, count=True)
def main(verbose):
    print(verbose)


# add an option
click.option('--times', '-n', type=int)(main)

# overwrite the callback
callback = main.callback
def foo(**kwargs):
    print(kwargs)
    kwargs.pop('times')
    callback(**kwargs)
main.callback = foo

main()