Could genetic modifications become hereditary over time? If so could they evolve over time similar to regular genes? For example making carbon fibre bones for whatever reason would they eventually become a regular genetic trait?
If the modification happens on someone's germline cells, it becomes hereditary.
Notice that modifying zygotes, or an embryo, tends to have much the same effect, since germline cells will develop from those.
Once it becomes hereditary, such modified genes will follow all the same rules as any other genes.
Remember, every single gene existing in nature today is a mutation from some previous gene, all the way back in history to the very first RNA strand.
If you're just doing something localized though, like infecting only your liver with a modified adenovirus to get more alcohol resistance, then your kids probably won't get it from you.
They can. Maybe.
As @Renan pointed out, as long as you modify the eggs and the sperm producing cells, it can be passed on.
However, and this is the big question:
Can the embryo and/or the infant survive with the modifications. A lot happens in the first few weeks (and then over the first few years).
The common thought is that even zero-G will interfere with the development of the fetus because the chemical processes are so balanced for the process in 1G. It would take careful experimentation or great luck to get genetic modifications that allow for a viable fetus.
After birth there is a lot happening in a growing child. For example: if they grow too fast, their joints may not develop properly. Then we get into puberty and everything that happens then.
So, my answer is it is possible but not probable.