Managing keychain from terminal
Why?

The login keychain is for your user account. Moving that data to the system keychain would make your information available to all user accounts including 'Guest' accounts. Do you really want to do that?

I don't know if it is possible to do what you want, but if I look at my login keychain it includes my personal passwords, Apple ID, public keys (no problem), and private keys. These should never be made available to anyone. They are private for a reason.

Don't do this.