Trending @Accenture; June Appraisal

I have a small doubt that I wanted to ask regarding the appraisal process. Does this process gets closed in May end and we get to know our rating in June? Also can a supervisor change the rating after the closure and before the employee gets to know his/her rating? I am asking these trivial doubts because I have to ask for release from my current project just after appraisal and I want to be sure that it does not affect my rating. Also does doing some certifications in a different domain boost your rating or not?