Our user LastSword has released a very sophisticated mod, which we think is worth having a look at. The Scenario Generator allows you to set up any type of mid-game scenario, with further follow-up scenarios. There are also numerous more changes, like the introduction of a stacking system, removal of unique abilities, unique units depending on your development, and much more.
The creator LastSword describes it like this:
“Scenario Generator is recently released total conversion mod for civilization V. It converts the base map to “mid-game” situation by filling it with cities, units, improvements and diplomatic relations based on one of five available rulesets (each based on era known from the base game). You become a leader of civilization for 25 years (100 turns) during which you have to stand the test of time. Scenarios can be played separately or continuously, mod will use information from previous eras to generate next scenario.”
You can find the mod on steam:
https://steamcommunity.com/workshop/filedetails/?id=2632664616
Or check it on our forum:
https://forums.civfanatics.com/forums/scenario-generator.617/