Time code column editing

So I have a large cue list and wish to edit the timecode which currently starts from zero to start from 6 00 00 00.

So I highlight the timecode column type +6000000 and hey presto every cue has changed it’s original numbers.

and there is no undo for this operation, so I have to go back and retype every cue timecode adding 6000000 to the original numbers.