Is there any way to change a password hint without changing the password?

dscl . -merge /Users/username hint "your password hint"
  • Replace username with the short name of the account you wish to modify.
  • Replace your password hint with the hint you would like to set for the account.

dscl is the Directory Service command line utility.
. is the local machine.
-merge allows you to add a new key to a record path.
/Users/username is the record path for the key.
hint is the key you would like to assign a value.
your password hint is the string value for the key.