The default behavior is to backup all instances. To exclude an instance from being backed up, add the following tag to the instance.
aws ec2 create-tags \
--resources i-1234567890abcdef0 --tags Key=Backup,Value=False
The default behavior is to retain backups for 14 days. To change the default behavior, update the CFT parameter with a new value. To change the individual behavior of a single instance add the following tag.
aws ec2 create-tags \
--resources i-1234567890abcdef0 --tags Key=Retention,Value=3