Is it possible to add an Argument to an python argparse.ArgumentParser without it showing up in the usage or help (script.py --help)?
Yes, you can set the help option to add_argument to argparse.SUPPRESS. Here's an example from the argparse documentation:
>>> parser = argparse.ArgumentParser(prog='frobble')
>>> parser.add_argument('--foo', help=argparse.SUPPRESS)
>>> parser.print_help()
usage: frobble [-h]
optional arguments:
-h, --help show this help message and exit