Vatican Website translation:
97. Appropriate instances are to be defined by the rubrics in which a liturgical service may be substituted for the divine office.
In particular cases, and for a just reason, ordinaries can dispense their subjects wholly or in part from the obligation of reciting the divine office, or may commute the obligation.
97. Opportunae commutationes divini Officii cum actione liturgica a rubricis definiantur.
In casibus singularibus iustaque de causa, Ordinarii possunt subditos suos ab obligatione Officium recitandi ex toto vel ex parte dispensare vel id commutare.
Slavishly literal translation:
97. Opportune commutations of the Divine Office with a liturgical action are to be defined by the rubrics.
In particular cases and for a just cause, Ordinaries can dispense those under their authority from the obligation of reciting the Office totally or in part or can commute it.
Having considered those obligated to the daily praying of the Liturgy of the Hours (arts. 94-96), the Council Fathers now consider how this obligation can be dispensed from for those for whom it would create an intolerable burden. (As illustration of this difficulty, I can report the case of a now-deceased priest of my own Archdiocese who was afflicted with a severe case of scrupulosity that only grew more intense as he aged. By the time he retired from active ministry, the affliction had reached the point where he would re-recite multiple times sections of his Breviary because he was afraid that he had not prayed them with proper attention. Eventually this repetition took over most of his waking life, so much so that those charged with his care petitioned the Archbishop to dispense him from the obligation of reciting the Divine Office daily. The Archbishop did so and simply encouraged him to spend some time in spiritual reading every day without making it an obligation lest the same set of scruples kick in.)
Notice first that the rubrics of the Liturgy of the Hours themselves may indicate cases where other liturgical services may substitute for the Office prayers. For example, the Easter Vigil takes the place of the Office of Readings for Easter Sunday and those who participate in the Easter Vigil are not bound to prayer Night Prayer on Holy Saturday.
Secondly, the Ordinary may either dispense someone under his authority from complete or partial daily recitation of the Liturgy of the Hours or may decree some substitution for it, such as spiritual reading or the recitation of the rosary.
Pray Tell readers may wish to discuss what circumstances might appropriately lead to the lifting of the obligation to recite the Office in whole or in part as well as what appropriate substitutions might be suggested when the obligation is lifted.