This is not so complicated. When a priest, brother, nun or sister is on leave, for whatever reason, he or she retains his or her title and may use it.
When a dispensation is granted, the person continues to be a priest. To be laicised means that you return to live in the lay state. However, you are not a layman. You will be a priest until you die. You cannot undo ordination. Your authority is taken away. However, if you choose to celebrate the sacraments, after a dispensation, they are all valid, except for absolution and marriage, because you need faculties for those. However, if a person is need urgent need of confession and you’re the only priest available, the absolution is valid. The Church supplies as long as there is no impediment.
Once you receive your dispensation, the Church commands you to lay aside the title and the religious garb and to live the life of a layman. However, there are restrictions that will never be lifted. You may not teach theology, be a lector, EMHC, or hold any public ministry unless the bishop authorizes it.
Fraternally,
Br. JR, OSF