Yes. With xml. The easy way would be to swap out whatever weapon he has in <AutoCreateEquipment> tags with your choice from coreweapons.xml (located in game's english / data folders ) .
You can make your own weapons as well if you want to check "use mods" and then can save all kinds of stuff in your mods directory.
I prefer to do it that way than modify my core files. So when I uncheck "use mods" I've got clean vanilla game again.
