Apply a function to content

function convert($content, $modifType) {
    if($modifType = "'") {
        str_replace("& #365;", "u'", $content);
    } elseif($modifType "x") {
        str_replace("& #365;", "ux'", $content);
    }

    // ...
    return $content
}

@EVAL
$myContentVar = $modx->documentObject['content'];
// what I want to modify in my content
return $myContentVar

@EVAL
$myContentVar = $modx->documentObject['content'];

if(isset($_POST['disp_type']))
{
	$_SESSION['disp_type'] = $_POST['disp_type'];
	setcookie('disp_type', $_POST['disp_type'], time()+365*24*60*60, "/");
}
elseif(isset($_COOKIE['disp_type']))
{
	$_SESSION['disp_type'] = $_COOKIE['disp_type'];
}
else
{
	$_SESSION['disp_type'] = '';
}

switch($_SESSION['disp_type'])
{
	case 'x' :
	$char_disp = array('cx', 'cx', 'Cx', 'Cx}',
			'gx', 'gx', 'Gx', 'Gx',
			'hx', 'hx', 'Hx', 'Hx',
			'jx', 'jx', 'Jx', 'Jx',
			'sx', 'sx', 'Sx', 'Sx',
			'ux', 'ux', 'Ux', 'Ux');
	break;

	case 'h' :
	$char_disp = array('ch', 'ch', 'Ch', 'Ch}',
			'gh', 'gh', 'Gh', 'Gh',
			'hh', 'hh', 'Hh', 'Hh',
			'jh', 'jh', 'Jh', 'Jh',
			'sh', 'sh', 'Sh', 'Sh',
			'uh', 'uh', 'Uh', 'Uh');
	break;

	case 'a' :
	$char_disp = array("c'", "c'", "C'", "C'}",
			"g'", "g'", "G'", "G'",
			"h'", "h'", "H'", "H'",
			"j'", "j'", "J'", "J'",
			"s'", "s'", "S'", "S'",
			"u'", "u'", "U'", "U'");
	break;

	case 'c' :
	$char_disp = array('c^', 'c^', 'C^', 'C^}',
			'g^', 'g^', 'G^', 'G^',
			'h^', 'h^', 'H^', 'H^',
			'j^', 'j^', 'J^', 'J^',
			's^', 's^', 'S^', 'S^',
			'u^', 'u^', 'U^', 'U^');
	break;

	default:
	$char_disp = array('ĉ', 'ĉ', 'Ĉ', 'Ĉ}',
				'ĝ', 'ĝ', 'Ĝ', 'Ĝ',
				'ĥ', 'ĥ', 'Ĥ', 'Ĥ',
				'ĵ', 'ĵ', 'Ĵ', 'Ĵ',
				'ŝ', 'ŝ', 'Ŝ', 'Ŝ',
				'ŭ', 'ŭ', 'Ŭ', 'Ŭ');
}

$char_src = array('cx', '{cx}', 'Cx', '{Cx}',
		'gx', '{gx}', 'Gx', '{Gx}',
		'hx', '{hx}', 'Hx', '{Hx}',
		'jx', '{jx}', 'Jx', '{Jx}',
		'sx', '{sx}', 'Sx', '{Sx}',
		'ux', '{ux}', 'Ux', '{Ux}');

$myContentVar = str_replace($char_src, $char_disp, $myContentVar);

return $myContentVar;