Does a divorce issued with the notional intention of pleasing one's mother, yet without a genuine intention of divorce, take effect, and does this fall under the ruling of duress or jest?

Divorce does not occur by mere writing unless accompanied by intention or utterance; otherwise, it does. Therefore, you are not bound by a divorce merely by writing, although it is preferable not to repeat such an act. Obedience to the mother in divorcing one's wife is not obligatory.