I thought you could do SDC if CE is available on the swap. If not you can go into ET but you lose the POUG fee. It is complicated after doing a POUG. For instance if you subsequently change your flight to a different date, you get to keep the POUG fee which goes towards any recalculation for an upgrade as part of the change, however if the new flights are cheaper again you lose the entire POUG fee, and I think you also lose it if when changing you keep the original cabin. As the OPs example is for a base HBO fare, however, any date change would need to be into a higher cabin to keep all monies already paid into a new fare. Obviously he only want to do a SDC anyhow.