I had a request from one of my users I have been struggling with: They want the global search to display the available quantity of an item. So if they search widget one it will show that and the quantity available. I have been having the hardest time trying to figure out how to even change theses fields as his are completely different from my saved search even in the same role.

If a user asked me that, I would tell them that's not the purpose of the global search bar. It's for searching across all records and accessing the correct record - not for showing details of a particular record. Instead, I would suggest building them a Saved Search or report that allowed them to filter by item.

The only way to kind of achieve this is by doing a global search with a prefix, like 'item: widget' and pressing Enter so it brings up the results of an item search, which is customizable. (The un-prefixed global search results page is not customizable; the only way you end up in the filtered results screen is if the only match for whatever you searched is one single record type - and this might be why you and your user see different things on the search, different permissions, different found results.) If you see on your screen 'Global Search: Item Results" then there should be a Customize button under it, and you could include Quantity Available in that.