Answer by shantanuo for single keypair for all regions

Upload the pem file that I need to copy to other regions and then ...

# chmod 400 /home/ec2-user/mydec15a.pem

# ssh-keygen -y -f /home/ec2-user/mydec15a.pem >> ~/.ssh/MySSHKeyPair.pub

#  aws ec2 import-key-pair --key-name mydec15a --public-key-material file://~/.ssh/MySSHKeyPair.pub --region us-west-2