As of patch 1.1: For those not focusing on the alchemy tree, it is possible to enjoy the Impregnation benefit without ultimately keeping the skill. One may put enough points in the alchemy tree to get Impregnation to level 2, then invest in other trees (not the alchemy tree) as much as possible to get Mutagen skills. In Chapter 3, before you meet The Operator during the quest From a Bygone Era, make sure you have all the mutagens applied already. Then accept his offer to reallocate your talents using the mysterious artifact. In the immediate talent distribution screen, re-pick all the skills in trees except the alchemy tree. The improved mutagens will remain even though you no longer have Impregnation.