preg_replace help and help with regex to handle escape characters

This question is related to a previous question but requires a refinement that I need help with.

http://www.experts-exchange.com/Web_Development/Web_Languages-Standards/PHP/Q_23491772.html

Problem: I am reading in a language file and updating it online and need to preserve the file formatting.
Mostly working except for situation with quotes in the replacement text.

I need a preg_replace that will update the one line searching on an array key ($token) + (n number of spaces or tabs) + '==>' + (n number of spaces or tabs) and replace it with the same formatting except with my new 'string here'.

Example array in file:

$LANG_MGE07 = array (
    'search_message'                    => 'Searched for the phrase \'%s\'. Found %s items (%s seconds).',
    'member_profile_pagetitle'                => 'Member profile for:',
    'watch_default_pagetitle'                  => 'Watch Content - Home page',
    'watch_series_pagetitle'            => 'Watch Content - Series View',
    'watch_episodes_pagetitle'          => 'Watch Content - Episodes View',
    'no_search_results'                 => 'No results found matching your search request'
);

A more extreme example:
    'register_failed_message'       => '<span style="color:red">The username or email you\\\'ve provided are already in use. Please try again...</span>',  

The existing function in my class that works fine (thanks Roonaan) except in the condition where the replacement text has quotes - escaped.

    function updateToken($token, $newvalue)
    {
        $this->_content = preg_replace('#(\''.preg_quote($token).'\'\s+=>\s+)\'[^\']+\'#i', '$1\''.$newvalue.'\'', $this->_content);
    }

Can this be resolved ?

Thanks!