And what exactly is the status of this custom? Does it obligate me as well? (My whole family and community wear a hat and jacket.)

In principle, a custom is binding. You can do a release from vows, or move to a place where this is not the practice, and then perhaps there is room for the reasoning that the local custom overrides the custom of one's ancestors.
As an aside, I will note that I have always wondered what good a release from vows does in this context. If following a good custom three times (why three? In the Shulchan Arukh it seems that even once is enough) is considered a vow, then the release cancels it. But that still does not get us out of the obligation of custom under “do not forsake.” Does the release really cancel the fact that this is how they practiced, or the obligation of “do not forsake”?
But what can I do—this is how people have practiced, and the custom of Israel has the force of law. And even if I had my way, I would not abolish it (= I would not permit their vow 🙂 )

Maybe the reasoning is that the local custom includes an exemption from ancestral custom for someone who has done a release from vows 🙂