If they're still showing as OPEN, then it means your ticket was not reissued into G/Z yet and the receipt will still show K... which thereby makes this a piece of cake.

Just call, tell the agent you want to re-use the same SWUs that are in there since they haven't been closed yet, have them change your flights to what you want and re-enter the SWU info into the ticket record. Since you're still within the 24hr period it makes it even simpler as there is no change fee or anything.

In the situation where your ticket was reissued and the SWUs show CLOSED, it makes it more complicated but it is possible to have them resurrected.