Oddbean new post about login | logout npub is uniquely determined by the nsec. you cannot have another nsec from the same npub
Have a look at pubky. They do base32 encoding without the very complicated, and never used, segwit checksum. Saves on code, bandwidth and complexity. This would be a better npub that would be not only uniquely determined but pass the test of indepenent invention: https://www.w3.org/DesignIssues/Evolution.html