Unfortunately, you can't apply a new key-pair to a running instance. You can only use the new key-pair to launch a new instance.
A possible workaround would be making a snapshot of the volume, create a new volume based on it and be able to use it back to start the old instance, create a new image, or recover data.
AWS has a guide you may follow to perform that operation:
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-key-pairs.html (just look for
Connecting to Your Linux Instance if You Lose Your Private Key).
It is not possible to add currently running instances to the Bitnami Launchpad for AWS. The Bitnami Launchpad only can manage instances launched by itself.