Hi Kathiresan,
You need to change the class files inside of that WAR, update the WAR file (just put the new class file inside of it and when WinRAR asks if it should update say ys).
After that you must undeploy the original pagebuilder from the server and deploy yours in order for this to work or else you will receive an error that the application already exists with a different vendor.
you deploy it by using the NWDS, there is a view there called deploy view.
If my answers helped you i'd be glad if you can mark them as helpful/correct so others who view the thread will also use them.
BR,
Saar