MyModelAdmin.php

<?php

class MyModelAdmin extends ModelAdmin {
  
	//..
  
	public function getEditForm($id = null, $fields = null) {
		$form = parent::getEditForm($id, $fields);

		$gridFieldName = $this->sanitiseClassName($this->modelClass);
	
		/** @var GridField $gridField */
		$gridField = $form->Fields()->fieldByName($gridFieldName);

		$gridField->getConfig()
			->addComponent(new GridFieldFilterHeader())
			->addComponent(new GridFieldSortableRows('SortOrder'));


		//here I want to do some extra actions after the GridFieldSortableRows has applied 
		//it's modifications to the gridfield!

		return $form;
	}
  
	//..
  
}