Hi guys,
find these lines in page.php:
if ($oPage) {
      $oTemplate->setPageNameIndex (BX_PAGE_DEFAULT);
    $oTemplate->setPageType ($oPage->getType());
   $oTemplate->setPageContent ('page_main_code', $oPage->getCode());}
 else {
 $oTemplate->displayPageNotFound();}

//add the lines below
ob_start();    
      $oTemplate->getPageCode();
    $pageinbuffer = ob_get_clean();
Now $pageinbuffer has all the code to display in the browser and you can do any changes by using php standard string replace functions as well as regex functions.
When you finish your changes just echo $pageinbuffer to send the page to browser.
To go through this route you need to be ready to fight and solve with many problems.
If you need more details my recommendation is to ask for professional help to develop a block from Boonex or AQB Soft. That way you will not expect future problems.
I am not a professional programmer :(