How to extend PrestaShop module without override core

[omixam 1]

Hello,

 

I want extend PrestaShop search for include category filter. Bu the PrestaShop Search.php class not has this option by default.

 

I also know that I can override PrestaShop classes and controllers

 

http://doc.prestashop.com/display/PS16/Overriding+default+behaviors

 

But PrestaShop forbid override module fo distribute through addons.

 

I need do something like the image attached. A dopdown for category list with text box by search.

 

How can I do this without override?

 

Can I create a new class or single php file in my module directory to extend Search behavior?

 

What other alternative has PrestaShop to do this?

 

 

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