Does Traditions custodes in any way change the position of the traditional rite of marriage as related to the requirement to observe canonical form? Can a Catholic still marry validly and licitly in the older rite? Would permission from the local ordinary be required?
Your question opens onto to several fronts. Let’s take care of the immediate question first.
The Apostolic Letter Traditionis custodes, makes no mention of either the Sacrament of Marriage or the ritual involved in the contracting of marriage for Latin Catholics.
TC states – as if it were a fact – that the current liturgical books are “the unique expression of the lex orandi of the Roman Rite”. That statement is, like any statement, obviously open to proof to the contrary. Gratis asseritur, gratis negatur.
In fact, several months later, the very same Francis issued an Apostolic Constitution (which has greater canonical weight than a mere Apostolic Letter), Praedicate Evangelium, in which he acknowledged and legislated for two forms of the Roman Rite.
Being faithful sons of the Holy Church we must more recent and weightier rulings as those in force now. PE does not mention any liturgical books other than the Roman Missal of 1962.
Several months later, the erstwhile Congregation for Divine Worship and the Discipline of the Sacraments answered several dubia that had been proposed… apparently. Those who … apparently… asked those eleven questions, and only they, are bound by the responses given, in which the Prefect mandates that the Rites for the Sacraments using the 1952 Rituale, may only be performed in personal parishes dedicated to the Extraordinary Form.