From a reader…
I am a seminarian. One of my family member is have a non-Christian wedding but wants me to bless her engagement at home. Is it okay to do so?
Even if the marriage were to take place in the Church, a seminarian is a layperson, and would have no more jurisdiction than any other layperson to bless an engagement. Doing so would have no effect on the engagement, and would probably imperil your continuation in the seminary.
Even though the blessing of an engagement is not exactly usurping a role exclusive to the priesthood (the so-called Book of Blessings, propediem concremetur, allows most “blessings” to be done by just about anyone) and would not suffice to invoke can. 1041, 6 making you irregular for the reception of orders, it might allow for the invocation of canon 1384 and open you to punishment for the illicit performance of some sacred ministry.
Don’t do it. Even if you think you really should. Even if you think it’s going to be really super secret and private.