From a recruiting perspective, I'd echo Alf's advice also when it comes to joining in one role with the hope of transfering to or combining another. At present we're gagging for WEOs and trying to fill billets in that role whereas unusually, we seem to be less desperate for Warfare Officers.
Obviously things can and do change but for now, whilst the option is feasible, for those with the luxury of chosing either should go for the one you want most. A Warfare Officer with an Engineering degree probably has a better chance of becoming an Engineering Officer than as an Engineering Officer wanting to go Warfare - based on manning requirements.
As we develop the Information Warfare cadre there will be more need and opportunities for Warfare personnel who understand more about Information Operations and how to use Communications to better warfare effect.
The days of the long PowerPoint PWO(C) are gone but it's going to mean far wider opportunity.