Create a new aaa authen profile for local authentication only. Set the vty 1 line to use the aaa profile for local only. This means that the first connection (vty 0) will use the normal authentication (keep this session open) and the second connection (vty 1) will use the local only. Once complete reset the vty 1 line to use your normal authentication method
The key is to always leave yourself with a method of returning authentication to your usual method if the local password is corrupt.
Hope this helps
You can open an SSH session, null route your tacacs servers on the device, then try and login with a new session. Keep that first session open in case the local username/password does not work!!