The JS files that you will probably need to modify are these -
If all you need to do is add a pathfield to the panel, you should be able to do this by modifying the TitlePanel.js. The way I have customized the slideshow component is copy this files to my app directory and change the xtype on the Slideshow.js when registering it.
So your custom component would look something like this -
/apps/mycomponent/slideshow/clientlib/js.txt (for JS libraries)
/apps/mycomponent/slideshow/myslideshow (your custom slideshow component - dialog/jsp etc)
Your js.txt would look something like this
At the very end of your Slideshow.js file, you will register your custom component like so
// register xtype
Do you have a sample code that you can share?