I'm moving this over to Issue 11695, which proposes support for a usage/help message template.

To customize the argument group names, the recommended approach is to create your own argument groups, and only put arguments there, e.g.:

parser = argparse.ArgumentParser(add_help=False)
flags = parser.add_argument_group('My Optional Arguments')
flags.add_argument('-h', '--help', action='help')
flags.add_argument('-v', action='version', version='1.3')

Then you'll get just the "My Optional Arguments" heading.