Right now, the only aspect of a population center that you can change via the GUI is which kingdom controls it. But that is not enough.
The parser often misses which region a PC is in. Or sometimes that info just is not available. If the user happens to know the region, it would be nice to update that info without having to manually edit the CSV data file. Ideally, this should extend to all the attributes of a population center
You cannot add a pop center that someone tells you about without manually editing the saved data. Minimum required info is map location, type, and name. The owner and region are also useful but not required. But if you have the rest of the info, you should be able to enter it as well.
Right now, the only aspect of a population center that you can change via the GUI is which kingdom controls it. But that is not enough.