The only arbitrary thing defined for a region is the max population. All the rest is procedurally derived from the actual properties of the region. It's pretty cool.
You did a pop rebalance in the past, nothing would prevent you from setting a standardized max pop, according to size of region and region type. You'd need a few different city "types", but it could work rather well. If you wish for max pop to also be procedurally derived.
