Most colleges won't predict you A*'s but some will, it's down to their preference and yes, unis are aware of this. You will not get an instant rejection for having an A predicted in a subject the uni is asking for an A* in, however, if the course and university are particularly popular and competitive then you may be at a disadvantage because they'll use that A as an easy way of deciding a short-list of students they want.
Where are you applying and what is the name of the course?