If you don't already have a custom writeable CC library, then you need to create one. You have to do this from the vault server ADMS console. Once you are logged in to that, you can right-click on the libraries and create a new one.
If you already have a custom writeable CC library, then you are good to go.
Next, you have to make sure that this library (new or not) is available in your project file. In Inventor, go to the projects editor, select your project file, then click on the Configure Content Center Libraries in the bottom right corner (just above the Done button). This will pull up a list of available CC libraries. Make sure the writeable custom library is checked.
Once your writeable library is available, then go to Manage tab > Content Center panel > Content Center Editor. This will launch the editor window that looks similar to the place from CC window. This is where what Blair said comes in. Find the fitting that is closest to what you need. In your case, that's probably the ASME 16.9 butt-welded fittings, since they are the only ANSI butt-welded option. Right-click the part family and choose Copy To > [whatever you named your custom library]. This will copy the entire part family with its family table and folder structure into your library. You can then edit it to your heart's content.
In this case, you will want to edit the family table and change the material, the wall thicknesses, change the schedule designation if you want it to show the "S", filename, part number, description, and anything else I forgot.
