[Idea]

is it possible to mod the m16(default) to a l9 sniper rifle with the l9 damage and sound?

Changing guns will only change the RoF and the model look.
Damage and Recoil will stay the same.

Yes it is possible to do that with sound. However, DAMAGE will practically never change during modding. It will just have the same Rate of Fire and NO SCOPE with the damage of M16. So no, damage wont' change.