To add or remove linked ZERO accounts from MetaMask, you don't need to scan the synchronization code again. You can just go through the steps described above and select any account you want to add or remove.
In the MetaMask browser extension, click on your account to open the "Select an account" screen. Then click "Add account or hardware wallet" → "Add hardware wallet" → "QR-based" → "Continue".
You can only remove hardware wallet accounts using the MetaMask browser extension, not in the app. A workaround in the app would be to disconnect your ZERO from MetaMask (using 'forget this device', see How do I disconnect my ZERO from MetaMask?), and then sync again but only add the accounts you want to keep.