Forgive my lack of mouse-drawing skills.
If a brisket is too big (long) for the food grate I will trim it to fit. But I don't cut completely through the meat. Let me explain and refer to the "3-year old's" drawing provided below.
With the brisket fat-side-up, make a cut about 3/4's the way through the thin "flat" end, leaving the end attached to the main part of the brisket. Turn the brisket over, meat-side-up, and fold the flap of meat over on top (meat-to-meat).
This will make the thin end of the flat thicker and help keep it from over cooking while fitting in smaller rigs.
I've never tried to get a brisket to "cook faster" because low-n-slow is the way to break down the tough meat fibers and make it tender.