There are now a great number of stage musicals based on musical films (often the Disney ones, but by no means always). Generally more songs have to be added for a stage version, as a half dozen songs can sometimes be enough for a film (especially if it's a relatively short one aimed at the family market) but a stage audience expects a full song score -- a dozen at least, plus some variety in the form of ensembles and finales.
However, On the Town is a different matter entirely. It's certainly not usual for a stage score to be thrown out and replaced by new songs! But at that time Leonard Bernstein was seen as an uncommercial proposition in movies, and his music was too "modern" (ironic, because in addition to this title song, the other Bernstein music MGM kept was the ballets, which are the most modern music in the show -- they've been turned into concert pieces). His next musical, Wonderful Town, inspired a musical film too, but in that case they bypassed the stage show completely and commissioned another team to do a completely different musical of the source material, My Sister Eileen (which is what they called the movie).
Only with West Side Story, filmed largely intact, was that "common wisdom" disproved: with all the promotion it received, the songs became widely known and liked, and the movie itself a huge hit. Anyway, there's nothing scary about On the Town: it's just uncomplicated fun. This production deserves to do well, and as I said, I already have my tickets in hand.