$this->registerHook('displayRightColumn') && $this->registerHook('displayHeader');

public function hookDisplayHeader() {
    $this->context->controller->addCSS(($this->_path).'***.css', 'all');        
}
    
public function hookDisplayRightColumn() {
    return $this->display(__FILE__, '***.tpl');
}
    
public function hookDisplayLeftColumn() {
    return $this->hookDisplayRightColumn();
}

<?php
class mymodulePageModuleFrontController extends ModuleFrontController
{
    public $display_header = false;
    public $display_column_left = false;
    public $display_column_right = false;
    public $display_footer = false;
    public $ssl = true;

    public function postProcess()
    {
        parent::postProcess();
        //...
    }
}