Either as a canon-divergence of the library scene, or at any other point, Lascelles gets the idea to punish Childermass for his 'insolence', and instead of just slashing his face, makes a serious attempt to cut out his tongue.

Whether Lascelles is successful or not, how much of a fight it is, is up to Anyone. I'd mostly just like to see him try, with some mouth injury!Childermass afterward, and maybe Norrell's reactions whether he's present for the whole thing or walks in during/after?