Doesn't bother me that they altered lyrics. It is after all a musical based on the film.
It's a little surprising at first if you're familiar with the original lyrics - minor things such as replacing "Since when did you become my mother?" with "I think I'll surprise my mother" in Carrying the Banner, but they all fit in well, its not like they have tried to force in anything modern for the sake of it.
I had no problem with Mary Poppins either, I do recall them stating that they needed to make alterations from the film version so it would have a better structure for the West End. Its not like they went in and just pulled things out of thin air, if I remember right Miss Andrews was in one of the other Poppins books, so just like the film, they are taking inspiration from the works of P.L. Travers.
Back to Newsies, I actually love some of the rearranging they've done. By the sounds of it, they have made a greater emphasis on the friendship between Jack and Crutchie (Santa Fe Prologue) which adds more to the story than the film did. ie. the lines where Jack is telling Crutchie he may walk properly out West. And the sentiment of the original Santa Fe is kept in the reprise. Not an easy balance to achieve.
Overall I think they've done an outstanding job with the show as a whole. I really do hope it goes international.