[Boofo]

Sure you can. As another example, here is one I use in the load_show_variables hook:

if ($vbulletin->products['adv_product_management4'] == 1)  
{  
    $show['modtools_apm'] = true;  
    $show['modtools_pm'] = false;  
}  
else  
{  
    $show['modtools_apm'] = false;  
    $show['modtools_pm'] = true;  
}

If APM is installed it will use that link. If not, it default to the vb product manager.

I also use the show variables in the navigation_tab_complete, but you have to globalize it in that hook, as well as $vbphrase if you use that there, too.