It sounds like what you're describing is a character whose playing with the quad containing the dynamic pair of fate/destiny:
From the definition for Fate:
The distinction between Fate and destiny is an important one. Destiny is the direction one's life must take, Fate is any given moment along that direction. So whereas one can have many Fates, one can only have one destiny. Fate describes a state of situation and circumstance that exists at a particular point in time. In other words, Fate is something of an outcome, or perhaps a step - just one of a number of Fates along the path of one's destiny. Characters often either make the mistake of assuming that they have only one Fate and are therefore stuck with it, or they mistakenly believe they can achieve their destiny without "passing through" unattractive fates that lie along the path. The nature of a Fate is that no matter how you try to avoid it, it tracks you. All options that you might exercise still lead to that Fate. That is what also defines Destiny as the limitations on free will that force you to arrive at your Fate no matter how you alter what you do or what kind of person you are. If we all knew the future, there would be no freewill.
So in other words, your character has a destined balance of luck. He can take advances on his luck, but he cannot change his ultimate fate to arrive at the "correct" balance eventually.
Whether fate/prediction/interdiction/destiny are your MC's UA or Critical Flaw largely depends on the role he plays in the overall story. Remember, the UA is what makes your MC uniquely qualified to aid in the achievement of the Story Goal. So does your MC's ability to manipulate his luck have an impact on the efforts at achieving of the OS goal? If so, is that impact positive or negative?
If your MC's ability to manipulate his fortune has no impact on the achievement of the OS goal, then that ability is not his UA, even if it is a nice piece of storytelling.