The key is that you need to know the passphrase to do it, if you don't know the password for the key then you can't remove the key since it cannot be decrypted.
ssh-keygen is the easiest method and openssl can be used to manually remove the key and output it to a new file, which you can then copy back over top of the encrypted file.
After that your public key authentication will work without any password prompt because it is no longer encrypted. Make sure you understand........
for ip in `cat fixlist.txt`; do
sudo -u apache ssh root@$ip "`cat iptablesrules.sh`"
In the above example we are going to execute the commands within the local file "iptablesrules.sh" on all the machines in "fixlist.txt". This is a great way of performing server maintenance in a clustered or cloud environment.........