You seem to be moving the goal post here
From your original post
As I showed above you would need anywhere from 256 thousand to 15 million individuals to even have one mistborn. And to get that you have to intentionally avoid anyone with Terris heritage to avoid the powers interfering with each other. This is further complicated because you need an allomancer within the last five generations in order to even have the chance to be one. TFE chapter 20.
Now even if you got two mistborn and they had children their offspring are not guaranteed to be mistborn, or even allomancers to start with, and so you have to go though even more genetics watching.
That is an experiment the likes of which has never been attempted before.
Increasing the amount of metalborn in the population is possible. Causing the reappearance of Mistborn or Feruchemists is possible but highly unlikely. Creating large numbers of Mistborn, Feruchemists or Fullborn would be neigh impossible