OMG, I just transferred two half-trip old Southwest awards to A+, then moved those 16 credits back to Southwest. I got two brand new half-trip awards with a full year of validity, replacing the 6 months I had had a few minutes earlier!
Also, I highly recommend moving 300 points to AirTran then 0.25 credits back to Southwest so that you have the seed to create a Standard Award any time in the next 2 years.