Best way to edit music videoclips: How add and audio track don´t linked to a video clip

When edit videoclips it´s very important the sync of the audio and music.

How can add a audio track to the timeline 2 (at audio section) and don't link it to any video clip, so if y change the video (in that I'm linking now) don´t lost the music or desynchronized the rest of the videos.

In other words, Its possible have a principal audio track not linked to any video clip?

Extra questions: why it for you the best way to edit videclips (music its the focus) in FCP 10.3?

Welcome Alex to fcp.co

Simple answer to both questions: drag the audio into the storyline!
Since anything is referenced to the music, the audio is the 'story'.

That's absolutely correct. I edit music videos on occasion where the music dictates what clips go where at what edit points. I drop the music into the Primary Storyline, and let all the video clips Connect to it. Very simple, very efficient.