Is there a feature that turns cities in the single cities sections into regions?

[TheoTownisdabest]

So I was generating a single city in the single cities section months ago, and i was building a city i for no reason named skull, not the emoji, but just skull, but I was trying to recreating something, but wondered, “If I complete the city, then I want to expand it.” I’ve been building my city for a total of almost a week straight and working for months. So is there a feature to transform a city in single cities section to a region? If there isn’t, then try adding the feature to do so because i want to turn my single city :skull to a region. And also, while adding the feature, how about adding like while your single city turns to a region, also adding more plots of cities, and i wanted to expand my city skull with more plots of cities.

my city i was working on: