Is there a way to make a macro for the addon Scrap so that I can click a button, while hovering over something in my bags, and add it to the list that Scrap uses? The reason being is I vendor green items from my garrison that don't sell on the auction house. With Scrap I can quickly vendor stuff without having to remember if that item sells or not.
So, you could likely write some lua to do this in your macro, but it would be complex -- there doesn't look to be a "what is the cursor over", just "what is in the cursor" API, so you would end up having to do a bunch more work to find the frame, identify the content as an item, etc.
What you *can* do out of the box is to drop an item onto the "sell junk" button at a vendor, which will toggle the junk/useful status directly. My mode of operation for exactly the problem you highlight is to (a) use auto-learning, and (b) use the drop-on-"sell junk"-button trick for things that I have lots of, or see frequently, and that have not auto-learned yet.
I believe that the Scrap LDB display can also do the same thing, if you use an LDB container that supports the item-drop API. (Don't ask me which ones do, I just remember reading about this feature, I never cared to use it.)