It seems to me that the general intent of these ceremonies is to protect against malign influence. Not like Protection from Evil, but more like a Turn Undead against very minor spirits that attempt to lead the faithful astray at critical moments. Each ceremony protects the individuals involved for a short period of time, no more than a week and often shorter, based on the specific activity being protected: opening prayers at a worship service protect against disruption of that service for its duration, for example. Most of the time, you don't need to worry about mechanics, but if necessary, here are the effects:
- blessed social interactions (like marriages): add double priest's level to reaction roll to indicate general initial mood of interaction.
- blessed endeavors (prayer at the beginning of a trip, dedication of a building): if there is an "X in 6" chance of an accident, reduce the chance of the first accident by 1 for every level of the priest (or subtract 1 from the first Situation roll.)
- protection from spirits/undead: treat as a one-time delayed Turn Undead; last rites and funerals specifically prevent the deceased from being transformed into an undead.