I would like to know if I'm able to play an event card that says "any phase" pre plot? For example I play an event card that allows me and my opponent to draw 1 card, I discard the event after use. Now I got 7 cards in hand he has 8, then we reveal plot cards I play Rule of Decree, does that plot card effect work? Can I do this?

The flowchart in the FAQ does show a window for player actions before revealing plots in the plot phase.