Population-related details are more or less flexible, and can be ported directly to the new system. However, the physical details of a world can be updated as follows. In terms of a player's experience, the size of a world is not terribly important. But a world's atmosphere is of paramount importance. A breathable atmosphere dictates one style of life, a polluted atmosphere another.
People live differently on vaccuum worlds, or on worlds with a corrosive atmosphere.
Universal World Profile first. Habitable worlds of size 4 are almost certainly Desert worlds which have been terraformed. These worlds take longer to terraform, but compared to the long history of the Imperium the task is manageable. A Vaccuum world of size 0-3 is probably a Rockball. Larger Vacuum worlds are possible, in the outer system, as Icy Rockballs.