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I think this is going about it the wrong way.
Just use the hook in the module.

Add Hook

$this->registerHook('actionPresentCart');

https://devdocs.prestashop-project.org/1.7/modules/concepts/hooks/list-of-hooks/

* find actionPresentCart for more info.

And hook function

public function hookActionPresentCart($params)
{
	$presentedCart = $params;    
    /* add your function for find values */

	$presentedCart['presentedCart']['subtotals']['shipping']['handling_cost_enabled'] = false;
	$presentedCart['presentedCart']['subtotals']['shipping']['handling_cost'] = floatval('5');

}

Tested in cart-summary-subtotals.tpl

{$cart.subtotals.shipping|@var_dump}

result: