We use Unikon Profi, when there is a holdover we always strike off each members clock first, then we go on to edit race and alter the date of lib and the result will be corrected automatically. You cannot alter the date of lib before you strike off clocks as the lib date will be different in the pocket clock and will not recocgnise the different date, hope this helps.
I think this is correct as it is a few months now since I had to do it ;D ;D ;D
We use East coast software to manage our clocks, so don't know if Unikon Club manager works like this or not