[Answer]-Database design, adding an extra column versus converting existing column with a function

Having a string-valued PK should not be a problem in any modern database system. A PK is automatically indexed, so when you perform a look-up with a condition like table1.pk = 'long-string-key', it won’t be a string comparison but an index look-up. So it’s ok to have string-valued PK, regardless of the length of the key values.

In any case, if you need an additional column with all unique values, then I think you should just add a new column.