I want to change a CC umbrella I found into a default replacement, and I don't know where to start. I'm hoping it's fairly simple (like changing an instance ID), but I may be way out of my league. Can anyone at least point me in the right direction to a tutorial or FAQ? I'm a little lost. Thank you.

I think the easiest way would be to clone the item you want to replace with the CC umbrella using s3oc. Once you hit the Clone or fix button you will see the Options panel that has a choice to Renumber/rename internally. IIRC this is checked by default. You need to remove the check mark from that box and then hit the Start button. Then you can export the meshes from the resulting .package in the usual way. Once you export those you would replace the original EA mesh with the new mesh that you want the item to have and then import it back into the .package. Depending on the object you're replacing you may have some .dds images to change as well but you could most likely borrow those from the custom umbrella .package.