Use boto to convert an S3 key to RRS

convert_key_to_rrs.py

# Convert an existing key in an S3 bucket that uses the STANDARD storage class
# to one using the REDUCED_REDUNDANCY storage class.  This uses the S3 COPY
# command to copy the key back to the same bucket.  The ACL is preserved.
import boto

# create connection to S3 service
s3 = boto.connect_s3()

# lookup my existing bucket
bucket = s3.lookup('mybucket')

# lookup the Key you want to copy in the bucket
key = bucket.lookup('myoldkey')

# change the storage_class of the key from STANDARD to REDUCED_REDUNDANCY
key.change_storage_class('REDUCED_REDUNDANCY')