I want to restate that what you suggest is
not a bad idea; it's merely not a good idea
for Tempestarii or Incursio. I really hope you can see the difference.
These creations have a certain focus that is strongly related to their concept, and altering that focus to allow for something they are not intended to be able to do is the same thing as changing their entire concept.
I do not want to do that,
because I am
relatively satisfied with these guys the way they are; I began with a certain image in my mind, and aside from some possible
minor tweaking, I believe that both Tempestarii and Incursio do a pretty good job of bringing that image to life.
I will
almost never throw something extra in "just for the heck of it", or "just because it's cool"; that just isn't the way I design something... and it eventually leads to a creation losing its focus. At that point, it is no longer the thing you were originally trying to make; it becomes something else. This can be a good thing sometimes (you come up with something creative and innovative), and a bad thing other times (your creation is poorly balanced, or lacks distinction/is generic).
Tempestarii can neither alter their bodies, nor pass powers along to their children genetically. It is not part of their concept, and never will be. It just doesn't fit with what a Tempestarii
is.
Incursio can both alter their bodies, and pass powers along to their children genetically. It is part of their concept, and always will be (so long as an individual Incursio is capable of physically doing either). It fits in with what an Incursio
is,
because the concept was designed around it.
Neither Tempestarii or Incursio can alter their biology in the specific manner you're talking about, and never will be able to; for the same reason they can't fly to the moon and back. It is not part of their concept, just does not fit into the concept, and doesn't really add anything vital enough to warrant being tacked on as an afterthought. Doing so would be poor design, and I try to avoid that whenever possible.
I hope this explains my reasoning in a way that makes sense.
I don't want you to think that I totally hate your ideas and am trying to shout you down or anything; I
did work in the body alteration and genetically inheriting powers into the Incursio concept as you suggested... I just did it in a way that makes the most sense to me, given the nature of the beings.
Altering their body composition from a purely biological standpoint, though, that really just does not fit in with this particular concept; it's something that would contribute more to a completely different creation.