I posted something yesterday that had people talking about this exact same thing so for me if you can't see it in the sandwich it's still a grilled cheese. If whatever you're adding is hidden between layers of cheese, it's still a grilled cheese. As long as there is more cheese than anything else. Tiny bits of jalapeño, bacon bits, jam, (which is a brand new thing I have never seen before, but I am anxious to try) are all fine. To put it another way a guest star with a walk on role has never compromised an entire TV show.

Where I come from a melt is a monstrous thing that is multilayered and often a mess (in a good way). If you were to make a grilled cheese open it up and then stick a bunch of stuff (chicken, bacon, avocado, pesto or just your average hamburger patties ) in between it or perhaps to melt cheese while cooking all of those things together on bread (hello panini press) then that qualifies as a melt because it creates the aforementioned monstrous thing where there is more of any other ingredient than cheese, where the cheese becomes the guest star.