Is your feature request related to a problem? Please describe.
Currently, PnP Core SDK provides support to overwrite list-items having same key-column.
Requesting to implement the same for the PnP-Powershell.

Describe the solution you'd like
Addition of an optional parameter "KeyColumn" which should be part of "Add-PnPDataRowsToSiteTemplate" operation

Describe alternatives you've considered
An alternative is to force developers to hardcode the KeyColumn value within the PnP-Template

Additional context
Kindly refer PR #2616 for the solution.