Hi,
I suppose that the "start of the URL" is the alias of the menu item.
That's because you have that code:
$menuClass = hikashop_get('class.menus');
$Itemid = $menuClass->loadAMenuItemId('manufacturer','listing');
if(empty($Itemid)){
$Itemid = $menuClass->loadAMenuItemId('','');
}
This sets the $Itemid variable to the id of a menu item which is either a brands listing or a categories listing.
And then, Joomla's SEF systme uses that id to get the alias of the menu item and use it at the beginning of the URL.
So if you want to have a specific text there, you should create a menu item of the type HikaShop category configured to display the brands, set in it the alias you want (brands) and use such code:
$Itemid = XXX;
where XXX is the id of that menu item.