How can I use PHP to add ACL Rules of a custom Usergroup to a core Component?

Question

Our component has a custom usergroup that is created at installation with UsersModelGroup. We need to add specific permissions to com_content for that usergroup without effecting whatever permissions may already exist for the component.

I'm familiar with creating a full set of rules for an article or category when creating the content, and for this task, could read the asset record, then use array manipulation to add my rule, but that seems a little brute-force. Is there a better way to do this?

Current com_content ACL Rules:

"core.admin":{"7":1},
"core.manage":{"6":1},
"core.create":{"3":1},
"core.delete":[],
"core.edit":{"4":1},
"core.edit.state":{"5":1},
"core.edit.own":[]

Using "123" as my custom user group, I need this set of rules to be in place:

"core.admin":{"7":1},
"core.manage":{"6":1},
"core.create":{"3":1},
"core.delete":["123":0],
"core.edit":{"4":1,"123":1},
"core.edit.state":{"5":1},
"core.edit.own":[]

Answer 1

Pending a more elegant solution, here's my somewhat neanderthal approach that works:

// Get the Asset record for com_content 
// I'm not assuming that the row id will be the same in every Joomla installation
$db = JFactory::getDbo();
$query = $db->getQuery(true);
$query->select('id, rules')->from($db->quoteName('#__assets'))
->where($db->quoteName('name') .'='.$db->quote('com_content'));
$db->setQuery($query);
$asset = $db->loadObject();

$rules = new JRegistry();           // Create a new Joomla Registry
$rules->loadString($asset->rules);  // Load the Current ACL rules into the Registry
$rule_array = $rules->toArray();    // Convert to Array for easy manipulation

// Set the ACL rules for Custom Usergroup 123
$rule_array['core.delete'][123] = 0;    // My custom usergroup cannot delete Content
$rule_array['core.edit'][123] = 1;      // My custom usergroup can edit Content

// Re-load the Rules registry with the modified rules array for saving
$rules->loadArray($rule_array);         
JTable::addIncludePath(JPATH_ADMINISTRATOR.'/libraries/joomla/table');
$row = JTable::getInstance('Asset');
$row->load($asset->id);
$row->rules = $rules->__toString(); // Save as string
$row->store();

Answer 2

Sorry, but I have no option then to post another answer. If I understand you correctly, you do install your own component, and want to add another option to com_content. So can't you just use

<access component="com_content">...</>

but as I said, New to Joomla/php I should not try to answer anything.