Create a new trail with the updated log file prefix, delete the original trail, update the existing bucket policy in the Amazon S3 console with the new log file prefix, and then update the log file prefix in the CloudTrail console.

Update the existing bucket policy in the Amazon S3 console to allow the security engineer's principal to perform PutBucketPolicy, and then update the log file prefix in the CloudTrail console.

Update the existing bucket policy in the Amazon S3 console with the new log file prefix, and then update the log file prefix in the CloudTrail console.

Update the existing bucket policy in the Amazon S3 console to allow the security engineer's principal to perform GetBucketPolicy, and then update the log file prefix in the CloudTrail console.