Swapping email programs in an active nurture program

I am currently in the process of making some changes to content in one of our active nurture programs.  One of the changes that has been requested is to flip flop the order of emails 4 and 5 in a particular stream. My initial thought was to just swap the priority of the programs so that offer 5 would come before 4 but now i'm not sure if that's the best solution.

1) If someone was sent email 5 before the swap, then the order is changed, would they receive email 4 again in the next cast or move on to email 6? Our email send campaigns only allow people to flow through once, so I don't believe they would be sent email 4 again but thought i'd confirm.

2) If someone is sent email 4 and then I swap the order of the email programs so that 5 comes before it, would they receive email 5 in the next cast since they have not been sent it yet?  Or, would they just move on to offer 6?

Any insights, advice or solutions on how to execute this change would be greatly appreciated!