Vocally, I'm not so sure. I would be pretty sure that Bernstein had a certain vocal type in mind and would not have changed that. (Sondheim has written about how hard it was to even get Bernstein to change the rhythm of the notes in "One Hand, One Heart" to make that text work.)
There's a section of the Tonight Quintet that Chita sang an octave lower originally - it would seem that Bernstein would rather have had that than to rewrite the part itself. To contrast, Sondheim has talked about how he actually changed his original melody for "Worst Pies" to better accommodate Lansbury's range. Also, he had originally conceived Fosca as a soprano - he changed that when Donna Murphy auditioned. But somehow I assume that Bernstein, who was thinking in an operatic vein, definitely wanted Maria to be a lyric soprano.