No that's not what i meant.
My video quality on the preview is fine, the problem is that i don't know a way to save my changes (synchronized) to a new file WITH the same quality from the original video.
I know that i can export the media, but when i do, Premiere must re enconde the video (which downsizes the quality a bit).
The video is an H.264 MP4 format and i've tried to raise the bit rate, but the output video always loses a little bit of quality (visible quality).
No you can't. Most mpeg formats mux audio, meaning that the audio bits are stored between the video bits. If the audio is stored in a seperate track, it can be done, it is called smart render. Supported formats can be found here: http://helpx.adobe.com/premiere-pro/using/smart-rendering.html