Move pivot from prefab or spawn it from child

I don't know how to ask this question. I have a modular level generator that spawns prefabs. I have a prefabs that is 10 points long in X(figure A), so I spawn another from a gameobject position inside that prefab that is a spawn point 10 points after the origin from this prefab(point B). Having a controlled size works fine, but I want to add prefabs with different forms, they would have different sizes and their origin point would be somewhere else. My question is, can I a) Spawn the following prefab using a gameobject position inside such prefab. For example, where prefab A ends prefabs B begins. Something like

 LLLLLL|LLLLL
       |
 LLLLLL|LLLLL 

where the | would be the spawn point of the next prefab.

B)Move the prefab origin point so I can always spawn it from the same position without having to hard code the spawn point position for each prefab.

Thank you people!