Settler should be able to join city

[youtien]

After Mongol invasion era, I often raze cities then use a settler to rebuild, in order to get free buildings, but this is too brutal. I would like to let settler have a "join city" ability, with that, a near-destroyed city can get all free population & buildings provided by that era.

 

[BenZL43]

It should be limited to conquered cities within 3 turns with only 1 or 2 population only, perhaps, to reduce abuse of settlers...