Wow, did you charter a whole plane? Is it some sort of reunion? How do you remember all their birthdays and anniversaries?!

Depends upon the type of discount code it was. The ones openly issued for various routes/regions are time limited so would not be available for use again unless they've not expired. If it's one from a broken IFE or other inflight compensation, you should be able to have the agent apply a similar discount on the rebooked ticket. However, if you plan to use it for a different new booking, it may not have further life.

However, for the difference of 2-hours, why bother changing the feeder flight and paying all the change fees and possible higher fare? Buy them two MLL passes.