Is there no way to edit a map from a save file?

[The Tollan]

I started up a game recently and one AI civilization has built a city on Flood Plains so now that tile has lost the flood plains status. This is a little bit annoying even though it probably won't my civilization directly. It would be useful if I could change it back or at least change some other desert tile to have flood plans status (by adding a river on the edges or directly changing it).

Is there any way to do this or is it still not feasible?