Typically an actual key is effectively just a very long pseaudorandom binary blob and the passphrase is just used to unlock the actual key. This means you can add a new key just by encrypting the actual key with the new passphrase
Typically that is also the way you can use multiple accounts to unlock the same hard drive encryption. You just encrypt the actual key with each of the account passwords.
Typically an actual key is effectively just a very long pseaudorandom binary blob and the passphrase is just used to unlock the actual key. This means you can add a new key just by encrypting the actual key with the new passphrase
Typically that is also the way you can use multiple accounts to unlock the same hard drive encryption. You just encrypt the actual key with each of the account passwords.