Set tech status.
> Unobtainable : if the tech is not a shadow tech, setting it unobtainable will remove it from the building where you can find it.
> Obtainable : will make a tech available for the civ. For example you can make Topkapi available for the French (originally unique to the Ottomans)
Active : this is what you are looking for.
(fr) Regarde à travers et vois le cygne et ce qui vit au-delà de l'au-delà.