First order they try to balance profiles, second order they look at why person X versus person Y in the same profile . Competing offers definately boosts your chances as more than one school thinks you are recruitable after your MBA. Since 2008 MBA applications have become about employment figures and showing a higher number of recruits on graduation. Booth and Tuck went up the ranking just based on few fractional improvement in employment numbers.
Significant updates help if there was genuine weakness in your application, like less experience or weak GMAT or some behavioral issue. If you say you got promoted in your company, there is no way for them to verify that unless you provide a recommendation.
UCLA is really struggling with attracting quality applications as its ranking is going down.
Again these are just my thoughts