Since Drivepool becomes read only when you have a missing disk I don't believe you can add a new disk like you want to.
But you can still stop drivepool service and swop in your new 2TB drive (if new initialize and format via windows) and copy the content of the poolpart.xxxxxxxxxxx folder on 500GB to the new drive. Shutdown server remove new drive readd old, start server then force remove 500GB drive (might be able to just remove 500GB drive and leave new 2TB when reinstalling old 2TB drive and just remove missing disk from dashboard). Then add new 2TB disk. Move content into new poolpart.xxxxxxxxxxxxxxxxxxx on new 2TB.
DP really has nothing to do with a copy from disk to disk in this situation. Just ensure the service is not running during this process.