Get root access without going through replacing things? I'm totally new to rooting and I would like to simply have root access to my phone. I don't want to do any customization whatsoever to the insides of it. Is this doable? I mean like, in terms of a PC, I want to simply give my limited user account an administrative privilege.

Sorry if this seems weird and all but I'm unfamiliar with these grounds.

If it makes answering a little bit easier, my phone is an Xperia Active and here's the information I can find inside Settings > About.



For example, I only want to change the default media sounds stored inside the internal memory. Things like that.
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.