Hi,
I suppose what you're saying is false. The system must be reading this file, otherwise, you wouldn't have had the error you reported in your first message in this thread. What I think is probably happening is that the modifications you want to make are in the secondary classes of this filter.override.php file.
Adding the "Override" suffix to the class name will only work for the main class in this file.
For the other classes, where you want to add your div, you also need to modify the methods of that main class which load the other classes.
Search for the line:
$classType = 'hikashop'.ucfirst($filter->filter_type).'Class';
in your file. You should find three occurrences.
After all of them, add this code:
if(class_exists($classType.'Override'))
$classType .= 'Override';
That way, it will support the Override suffix for the other classes. And you'll see your modifications being taken into account.