Anyone know if it is possible to modify era progression? Either to add more techs required per era, or only allow techs from the most recent era to count for the next one?

In SimulationDescriptors[Class].xml line 601 you can change the value which is the requirement to pass to a new era.

You have the technologies cost you can manage too.

Currently, all technologies from all era are taken in account in order to pass to a new era. You can also change this in the xml.