nice video, altough I think he overthinned the paint making more work for the same result.
And altough it won't help you here, but lately for things like that nose/coloring of folds I've been using pigments/pastels more and more. They are quite transparent and the transitions are soft without a lot of work.
But as said, to darken a whole SM it's not feasible, here remains the good ol' glaze (altough if you like to experiment, then 'dusting' them with an AB from 'far' with high PSI could help both by being thin AND fast, but I'd thin with some retarder to stop the paint drying mid-air)