If it's actually lacquer, the crack can be sanded out, and lacquer applied over it, and then smoothed and re-polished. Lacquer, unlike poly finishes, becomes part of the previous layer, so "fixing" mars, scratches, cracks, etc, is theoretically easier than dealing with damage to a poly finish.
The trick though is you need to find out specifically what lacquer was previously used. If it's truly a clear, nitrocellulose lacquer, that's pretty easy to do - you can use Deft lacquer. You also need to know how to polish a lacquer finish, i.e., wet sanding to level and polish, and then to do a final polish with something like 3M Swirl and Haze remover.
Here's another question. Is the lacquer cracked, or checked? Checking is hundreds of little cracks all over the finish. If that's the case, the only way to "fix"it, especially if there is a lot of checking, is probably to strip and refinish.