I was wondering if the ugrad-confirm@columbia.edu email can be used for updating the college on accomplishments achieved after the application has been submitted. For instance, could/should I let them know that I won an all-state audition for my instrument?
Yes. You send any required documents to: ugrad-confirm@columbia.edu. Please note that they will not reply back to any material sent to this address. Unlike skieurope, I have no idea whether or not it is too late for anything to be added. I cannot say because I don’t work at CU. However, I do not think your update is unique enough to give you a boost.