Hi kritica,
In general, Business Schools tend to accept noteworthy, 'updated' application information after an application has been submitted (such as a new/higher GMAT Score, a promotion at your work, a major award, etc.). That having been said, you have to remember that you get just one chance at a 'first impression', so you do not want to 'rush in' an application if it's likely to get 'wait-listed.' If your application is not 'fantastic' in some way, then you should not submit it - you would be better off continuing to study and working to improve your GMAT Score (and improving any other areas of the application that you can - such as your Essays) so that you can apply with a much stronger application during a later Round.
If you know which Schools you plan to apply to, I suggest that you contact each of them and ask your specific questions. I'm sure that someone in the Admissions Office will be glad to answer any questions that you might have.
GMAT assassins aren't born, they're made,
Rich