@noakes_eng
Ah! Thanks for the clarification. To do this, what you need to do is open or place any size of the fitting from the Content Center, and save it "As Custom", so that it is no longer a library part. Instances from Content Center that are placed "As Standard" are not editable. Once you have the part available, you can make any changes to the geometry, or to the authoring. Once you have made those changes and saved the part, go back to the Family in the Content Center Editor. Right mouse click on the Family, and select Replace Family Template. It will ask for the new template, and you will find and select the fitting that you just modified. If it all goes well, the changes you made should propagate to the entire Family table. In my experience, I found it best to make simple changes, and not too many at one time. I think Inventor gets confused if the new template is drastically different from the original and the replace function may fail. In your case, just changing the engagement should be fairly simple. Bear in mind that any changes will affect all instances of any size placed from that point forward. If you still need this fitting with the original engagement, it might be better to make a copy of the Family, and keep both available side by side.
I hope this helps!
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Chris Benner
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