We have content on some of our partner's websites like the Chamber of Commerce, etc. I would like to have better tracking on this data and was considering adding UTM tags to them. If we modified these backlinks with updated UTM tags, would that hurt our existing backlinks?
Adding UTM tracking to a URL effectively changes the signature of that page. In fact, technically speaking, the following pages are different:
And this applies to any query parameter, regardless of whether it's a simple tracking string or not.
UTM tracking parameters are well known, since Google Analytics is very popular. This means that, for sure, Google is able to recognize the parameter and ignore it causing the two URLs above to be treated as the same page.
However, to explicitly instruct the crawlers about the canonical page, you can use the canonical link tag.