@Biker: Indeed. I've just checked and light_center is not the light_origin. I never noticed that So creating a new entity def if you want the light origin to differ is really the only way it seems. However, I don't see the neccessity to have the same light to have different origins. That would only be inconsistent it seems, but that may just be me.
@Judith: The entity itself is not a light. You can see this by the entity not showing a light radius. The light comes from the attached entity (called flame). So if you want to change the texture for example you have to use set ... on. For example "set texture on flame" "lights/gathers/hammer_ornaments". You will see it works.
I agree that working with def_attached entities is not optimal yet. It would be nice if they would be previewable, and if one could alter settings on def_attached entities directly. But this would require code changes both in DR (at least a new gui that does something simlar like it's done in UE) and TDM (the way spawnargs are read or what gets understood by the engine might need adjustment). So it isn't impossible, but it is yet another objective on an already long list of stuff that "needs" implementation (according to what people assume needed) for a very limited amount of coders. And in this particular case we are not talking about something game-breaking, but more of a comfort function. So unless any coder consider it neccessary or anyone considering it neccessary becomes a coder, it is likely it will stay like this for a while, if not forever.