The big thing that I remember about capital punishment had to do with the Catechism, which is also a big deal, but not Canon Law.
It is possible that he did mess with Canon Law in conjunction with capital punishment, but I doubt it.
Francis does manage to mess a lot of things up a lot of the time, but he doesn’t manage to mess everything up all the time.
Sometimes he can make a mess without involving Canon Law.
It is possible.
If papal approval is not granted in forma specifica, then it is deemed in canon law to have been given in forma communi. Consequently, one cannot, strictly speaking assert in canon law that the Pope is the author of the change that has been made to the Catechism, even though it has been confirmed by Cdl. Ladaria in the newly released Letter of the Congregation for the Doctrine of the Faith to the Bishops of August 1, 2018 that Pope Francis did request that paragraph no. 2267 be modified according to his indications. Cf. Letter, in OR, August 3, 2018, page 8.
Canonical Effect of the Change. Since prudential judgments are referenced expressly in substance in canon 747, § 2 of the Code of Canon Law ("to render judgment concerning any human affairs insofar as the fundamental rights of the human person"), and since one cannot be bound by the stricter interpretation positing that the Roman Pontiff has ordered that the death penalty be held henceforth as an intrinsically evil act, by reason of the ambiguity of the novel term "inadmissible," the norms of canons 750, §§ 1 or 2, or 752 CIC, cannot be applied to bind the Catholic faithful under penalty, neither pursuant to canons 1364 or 1371, 1°, because we're not dealing here with a doctrine governed by canons 750, § 2 or 752, nor in conformity with canon 1371, 2° CIC, because no singular precept or prohibition imposed upon a Catholic with canonical admonition having been duly issued to him and violated is at issue, for the new formulation approved by Pope Francis enunciates a change in the prudential judgement of a general nature contingent upon perceived changes in the temporal circumstances of the State's ability to safeguard the peace.
The Devil Is in the Details: Pope Francis Changes Catechism on the Death Penalty