In his work with the yanomamo, chagnon traded manufactured goods like matches, fish line, axes, and machetes. does this change a culture? should he have traded tools/weapons with a culture known as "the fierce people? "

Yes, these items change a culture.

As a researcher, Chagnon was studying the "fierce people". His research revealed his perceptions of a tribe characterized as uncivilized and barbaric. He introduced new technology into the culture which did change the culture of the group.

Any new technology or material culture items introduced into a society will change the overall culture. The Native American tribes in the US experienced cultural change when horses were introduced for hunting and guns were introduced for hunting and war. When new technology is introduced to any culture whether from the outside or in, cultural change will occur.