An exchange can add as many admin accounts or broker accounts by converting a member account to either broker or admin.
An account can only have one status: member, broker or admin.
If you want to make a broker account an admin account, then remove the broker status to make it a member account again, and then make the member account an admin account.
One admin account must be a default admin, or nothing will work, as each exchange must have a default admin account, which links your default email address to AWS Simple Mail Service to send transactional emails + is the default admin account is the account that will receive all trade fee deposits.
To initiate an Amazon SES validation email, which is required to send system emails from VB, simply login as the default admin, then send an email to a member, which should trigger an SES validation email from Amazon sent to your email address to complete the validation.