When a musical is first written and performed, they put it on 'out of town' (not in New York), so that they can guage audience reaction, what gets laughs, what doesn't, what songs work well in the show, and what songs the audience don't seem to like etc. This allows the show's producer, director, and writers to make changes(=titivate it) as they develop the show, ready for Broadway.
The critic is saying, yes, there are changes that can be made, perhaps to the diagogue, perhaps change a cast member who is not right for the part. But whatever else you try to do to make this show a blockbuster, the score (music and lyrics) is so bad, it is the major disadvantage of the whole production, and as a liability, would in itself stop this show from being a hit on Broadway.
Student or Learner