Blessings are acts of divine worship and sacramentals (cc. 1166-1172). They are different from consecrations and dedications (see cc. 1206-1208). Blessings can be given to Catholics, catechumens and even non Catholics, unless there is a prohibition of the Church (c. 1170).
They can be validly given according to Canon 1169, “§1. Persons who possess the episcopal character as well as presbyters to whom it is permitted by law or by legitimate concession can validly perform consecrations and dedications. §2. Any presbyter can impart blessings, except those which are reserved to the Roman Pontiff or to bishops. §3. A deacon can impart only those blessings which are expressly permitted to him by law.”
The approved Ritual books would give particular details about particular blessings as governed by liturgical law (c. 2).
There are two kinds of blessings.
The first is a constitutive blessing. Like a dedication, it can make a place or object sacred, i.e., set aside for sacred purposes. Some examples would be a cemetary, a chalice and paten, the oil of the catechumens, the oil of the sick.
The second is an invocative blessing. It calls the favor and protection of God upon a person, place or thing. However, it does not change the person, place or thing being blessed.
The blessing of someone who is baptized, and therefore already consecrated, would be an invocative rather than a constitutive blessing.
Deacon John M. Cameron, JCL
Lansing, MI