ansible2 custom module, discussed at https://www.reddit.com/r/ansible/comments/4hpx4z/manually_changing_a_config_file_through_ansible/d2rwm7i

directadmincfg.py

#!/usr/bin/python
import os
from StringIO import StringIO
from ConfigParser import ConfigParser, NoOptionError


DOCUMENTATION = '''
---
module: directadmincfg
short_description: Sets options to a direct admin options conf
description:
     - Sets options to a direct admin options config
       Returning a list of changed options (with before and after values),
       as well as a flag indicating that the software should be recompiled
requirements: [ ]
author:
    - "bibby"
options:
  dest:
    description:
      - 'path to the file being managed.'
    required: true
    default: '/usr/local/directadmin/custombuild/options.conf'
  options:
    description:
      - A dict of config options to apply set within the config file.
        New additions are cited as changes.
        Does NOT remove unmentioned items.
    required: true
'''

EXAMPLES = '''
# set some options to the config at the default location
- name: options test
  register: reconfigured
  directadmincfg:
    options:
      foo: yup
      bar: nope
- name: recompile if needed
  shell: /bin/true
  when: reconfigured.recompile
  notify: recompile direct admin
- debug:
    var: reconfigured
'''

recompile_options = ['bar']
FAKE_SECTION = 'fakesec'
DEFAULT_DA_CONFIG = '/usr/local/directadmin/custombuild/options.conf'

# http://stackoverflow.com/questions/2819696/parsing-properties-file-in-python/2819788#2819788
class FakeSecHead(object):
    def __init__(self, fp):
        self.fp = fp
        self.sechead = '['+ FAKE_SECTION +']\n'

    def readline(self):
        if self.sechead:
            try:
                return self.sechead
            finally:
                self.sechead = None
        else:
            return self.fp.readline()

def main():
    module = AnsibleModule(
        argument_spec = dict(
            dest = dict(default=DEFAULT_DA_CONFIG),
            options = dict(required=True, type='dict'),
        )
    )

    params = module.params
    dest  = params['dest']
    options  = params['options']

    changed = False
    changed_options = {}
    recompile = False

    config = ConfigParser()
    if os.path.isfile(dest):
        config.readfp(FakeSecHead(open(dest)))
    else:
        config.readfp(FakeSecHead(StringIO()))

    for k, v in options.items():
        try:
            n = config.get(FAKE_SECTION, k)
        except NoOptionError:
            n = None

        v = str(v)
        if not n or v != n:
            changed_options[k] = dict(before=n, after=v)
            changed = True
            config.set(FAKE_SECTION, k, v)
            if k in recompile_options:
                recompile = True

    config_str = StringIO()
    config.write(config_str)

    # chop fake section header
    lines = config_str.getvalue().split("\n")[1:]
    with open(dest, 'w') as f:
        f.write('\n'.join(lines))

    module.exit_json(changed=changed,
                     changed_options=changed_options,
                     recompile=recompile)

from ansible.module_utils.basic import *
if __name__ == '__main__':
    main()