That is supported on at least Android (I think it is on iOS as well, but I'm not 100% sure). When you switch the backup options from High-Quality to Original qu

That is supported on at least Android (I think it is on iOS as well, but I'm not 100% sure). When you switch the backup options from High-Quality to Original quality you should get a prompt asking if you want to re-upload the photos on your device in Original Quality.