Ive just had a go myself trying it and i can confirm success. However I have found it easier adding plugins, which can be added to that product you have. I will give it a go so *deep breaths*
1) You need to add a plugin first.
Code:
Go to admin CP > Plugins & Products > Add Plugin
2) Info as follows:
Product > showroster hack
Hook Location > online_location_process
Title > Showroster WOL Process
Execution Order > 5
Plugin PHP Code >
Code:
if ($filename == 'showroster.php')
{
$userinfo['activity'] = 'showroster';
}
Plugin is active > Yes
3) Add another Plugin:
Product > Showroster hack
Hook Location > online_location_unknown
Title > Showroster WOL Display
Execution Order > 5
Plugin PHP code >
Code:
if ($userinfo['activity'] == 'showroster')
{
$handled = true;
$userinfo['action'] = 'Viewing Clan / Guild Roster';
Save both templates & then your done.
Alternatively, I made you a new product with it included. Simply overwrite product & your done.
BEWARE: If you are upgrading then backup those templates! I would advise you to do it the manual way!
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I have tested it and spent a good few hours developing it so this better pay off! LOL
NOTE: If you install the product, then it uses "Viewing Guild Roster" as the status. You can change it (if you are like me and have a clan) by going:
Admin CP > Plugins & Products > Plugin Manager > Showroster Hack > Showroster WOL Display
then you can change the code by choosing edit 
All the best mate, I hope it helps you like you have helped me
Matt