Carbon fiber parts over 15 years old with a yellowish appearance.
- How to make it look new again?

- Sanding the entire surface and applying a new clearcoat will solve?

No,the "yellowing " is ageing through the resin not just on the surface 

It can be possible, it depends how bad it is. You have to remove all of the yellowed resin, so sometimes this can mean you hit fibres before you get rid of it and in this case theres nothing you can do. However a lot of the repairs ive done, the yellowing is very bad because the part has a heavy coat of resin on the surface, and if you remove that then the yellowing isnt noticeable anymore and you can reclear it and get another few years out it. This steering wheel I did is a good example: 

Before:




After: 

I am going to risk this sanding technique to remove as much of the varnish and yellowish resin layer as possible.
I'm going to risk the method of pigmenting the clearcoat with black, the part will have a slightly darker carbon fiber, I believe it will hide the yellow tone better.

Hanaldo, Congrats, It was very good!