As far as I know, once you submit a degree (or in this case, a photocopy of it) with an apostille that meets their requirements, you supposedly won't have to do it again, as long as you remain in Korea and transfer to a new job or renew your contract.
Here's another question for anyone: I keep hearing about how they have relaxed the new paperwork rules for people who are transferring their visas in 2011, as long as it is their first transfer since the time of the paperwork requirement change effective on Sept. 1st 2010. Some people who have transferred or renewed (in other words, they aren't newcomers to Korea) have posted that their immigration offices didn't require all of the new paperwork and won't do so until 2012.
Does anyone have any experiences to confirm this?