Thanks for the clarification Beagle, but
An ex-UAS pilot would need to transfer all his/her flights into a civil personal flying logbook flight-by-flight in order to log the full 'civil' flight time. But this is a complete and utter PITA and the hassle involved for a low hours pilot simply isn't worth it.
Up to him, but I would think it well worthwhile starting a new logbook and adding the reglemented taxi allowance to each flight. IIRC, it is ten minutes, so if he has (say) fifty hours and fifty flights, that adds another 500 minutes, or approximately eight hours. That's quite a lot of money saved if hours-building for subsequent civilian qualifications.
I always recommend students who envisage becoming professional pilots to start from scratch with a good quality logbook (eg Jeppesen) rather than those PPL logbooks issued by the aeroclubs.