Get root access without going through replacing things?
Follow the guide in this thread to root your device. Xperia Rooting Tool - xda-developers

Rooting would install a Superuser app for you which will monitor apps which require root access. You can then install a app like Root Explporer to access your device's internal memory, just press Allow when it asks for root access. 

I believe you can find system media files inside the path /system/media/audio/, although it may change with devices or firmware versions. And don't forget to click on R/W on top in Root Explorer when you are deleting or replacing files to enable Read/Write Mode.