Do the feats Probability Manipulation and Evaluate The Outcome allow you to affect percentile rolls? Also, does Focus Of The Modron work with actions that take more than one round to complete, such as casting a scrying spell?
Guvner Probability Feats
Probability Manipulation specifically refers to "attack roll, damage roll, caster level check, or skill check", none of which are percentile rolls.
Evaluating the Outcome does, however, appear to apply to any roll, including percentile rolls (though an Intelligence modifier is proportionately smaller for such rolls).
I think Focus of the Modron looks like it works for long actions, yes. Of course, a -5 to AC is nothing to sneeze at if one is performing a multi-round action in combat, so I would certainly say the cost balances any gains. Your GM's interpretation is final, of course.
It would probably be too powerful to allow these feats to affect percentile rolls, since those are either spell failure chances or teleport errors.
The reason I asked about Focus of the Modron is because it says you must stand still for 1 full round (they probably meant helpless), then perform the action. But what difference does 1 round make if you're casting a scrying spell that takes a full hour? I think the feat assumes you're performing an action that takes no more than 1 round.
For longer actions, I'd suggest you'd have to remain in the trance as long as it takes to complete the action. So, to improve your chances with a scrying spell, you'd have to be in the trance (and helpless) for 1 hour, then cast the spell for 1 hour. That shouldn't normally be a problem since you'd be casting scrying from a safe location anyway. The helplessness is designed so that if you use this feat in combat, your allies had better be very good at stopping coup de grace attempts.