I think it would be almost impossible to swap the platter on a hard drive without scratching it or getting any dust on it. If you have ever pulled open a hard drive you would know how easily the magnetic coating on the disks is damaged. Also, it is often difficult to actually remove the disks. The six hex screws holding the disk in are screwed in very tightly, and to turn them you have to clamp the motor down, so the disk don't spin. Even oil from your fingers would probably ruin the disk. In my opinion, just by a new drive, as they are very inexpensive these days.
And to swap a new disk into it, you would have to buy another of the exact same drive anyway.