Since the player's life total is checked only as the spell resolves, you can cast Hidetsugu's Second Rite targeting any player, regardless of life total. If the player isn't at 10 life as Hidetsugu's Second Rite begins resolving, it does nothing and finishes resolving. Note that since having 10 life is not a targeting restriction, the spell isn't removed from the stack for having an illegal target; it just won't do anything.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.