For convenience I had an id_rsa keypair and duplicated them with a new name. I may or may not use them consistently on different machines. (The reason was to keep an existing id_rsa on a machine I didn't own.) Today I decided to give them new passwords
ssh-keygen -f id_rsa -p. Just to make sure, I checked md5 on both sets to see that they were identical before and after. After I changed the passwords on the private keys, they were different but the public keys remained the same. Which is what I wanted.
How worried should I be that there are now two individual solutions to the public keys? In theory I could keep doing this couldn't I? So clearly there are multiple solutions. How many?