The IS auditor's independence would be most likely impaired if they implemented a specific control during the development of an application system. This is because the IS auditor would be auditing their own work, which creates a self-review threat that could compromise their objectivity and impartiality. The IS auditor should avoid participating in any operational or management activities that could affect their ability to perform an unbiased audit. The other options do not pose a significant threat to the IS auditor's independence, as long as they follow the ethical standards and guidelines of the profession.