First of all, we will need Jumi component or Sourcerer plugin for this to work. We need either of these because the main focus here is custom development outside of the standard modules or articles within Joomla.
You can find Jumi here...it's my favority extension to Joomla other than Breezing Forms.
~My little advertisement on Jumi~
*Jumi is a component that allows you to write custom php and js pages and load them into your Joomla site. So, if you are needing to add some AJAX or interactivity to your website, Jumi is the component for you. Jumi is compatible with J1.0, J1.5, and J1.6. With Jumi, you can add custom content to your modules, articles, etc...
New to Jumi? View these helpful tutorials here: http://edo.webmaster.am/jumi/tutorial
~Now, back to the good stuff!~
If you plug this in at the top of your customized php page, you will get the results you need only on the pages you add this code to.
$document =& JFactory::getDocument();
This will add the script and css file to the <head> tag for that particular page. Then you can feel free to modify that page without worrying about messing up the entire site.
Please view these two Joomla articles that will provide further assistance for you, if you should run into any trouble.