I see thank you....that's what I thought....so if someone wanted to be 100% sure that his/her current Core wallet couldn't be compromised should old back ups /passwords get into the wrong hands then creating a brand new Core wallet on a new pc and sending the Bitcoins from the current wallet to it..
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That's probably more than necessary.
Simply generating a new address after the password change and then sending the bitcoins from the wallet to itself at the new address should be sufficient so long as the computer isn't compromised with malware that will steal the new wallet and new password.
.then backing up and re-encrypting might be the way to go ?
You'll want to do that the other way around. If you backup first and THEN encrypt, your backup will be unencrypted AND your encrypted addresses won't be backed up. Instead you should encrypt first, then backup.
or to maybe buy a hardware wallet and use that instead ?.
Sure. If you want a hardware wallet, they are a great option.