#panels panelizer

I need to alter some of the $markup output from a panelizer node page? but hook_page_preprocess(&page) is giving me only $page['content']["system_main"]["content"]['#markup'] in rendered format thats why i cant change any of the desired html tags?how can i change this #markup? out of the content key of the $page array, there is node['panelizer']['page_manager']['display']['content'] but changing it dsm the change but output is not effected?what i am missing?or does panels or panelized pages dont preprocess like normal node pages?