Hello,
Unfortunately, I can't really assess your profile without knowing more information about you. Can you briefly summarize your profile? The GMAT is just one dimension of your whole application -- if the rest of it is outstanding, then the GMAT won't matter as much... if the rest is average, the GMAT will weigh a little more, and so on. It's a balancing act and you want to shine through as a capable, multi-dimensional leader. Your GMAT score is okay - not as high as these programs tend to like, but that doesn't mean you're out of the running.
As for whether they would accept an updated score after you've submitted your application. Usually not, but you can call the admissions office as an anonymous caller and see what they say. I could see submitting a score reflecting negatively on your application, that's why I suggest asking anonymously first.
Good luck,
Mili