Original arrival on thailand pass is dec 5 but friend rebooked for dec 10, and thailand pass showing it is valid until 2022. Can he still use his approved thailand pass qr code?

I thought it was only valid for 3 days from the info you applied with for flight / date changes?

He will need to apply for a new Thailand pass since his arrival date will be more than than 72 hours from the date on the Thailand Pass.