One Timeline - different grades/looks?

Is there a way to have one time line where it is completed with the grade, transitions, audio effects, blood sweat and tears

And then, re-do the colour grade with all the clips but leave all the blood sweat and tears unaltered?

At the moment with my level of skill, I just create a new timeline and then cut and paste my old project into that new timeline. The only problem is that stuff like my audio changes are removed and I'm back to Ground Zero.

Is there a way to have a project graded one way and then have the same project graded a new way AND I still have access to both grades with all the creative choices of audio still the same?

You can have multiple versions of a graded clip or clips. So you can switch between versions.

Reference manual that is available form help menu, Chapter 140 Grade Management

The Color page offers numerous ways of saving grades, copying grades, creating and altering groups of clips to share grades, rippling grades and adjustments, and managing multiple versions of grades.

If you are using a new timeline, in the media pool try right clicking on the timeline and choose duplicate. Check to make sure all the elements you say you lose are there.