
In this picture, what is the usage of the pronoun "you"? Can we use "subject pronoun" after "adjective",as in the picture "a different you".

In this picture, what is the usage of the pronoun "you"? Can we use "subject pronoun" after "adjective",as in the picture "a different you".
Advertising, exhortations, and other rhetorical texts often make a point of employing unusual constructions in order to seize your attention and make their points more memorable.
There's nothing ungrammatical in modifying pronouns. It's uncommon, because the ordinary use of a pronoun is to refer as briefly as possible to something previously identified. Here, however, you doesn't mean just the person addressed but the changeable nature of the person addressed: "a different you" means you as you might be, a person with different characteristics than you now possess.
This is, by the way, not a "subject pronoun" but an "object pronoun": you does not distinguish subject and object forms, but you here is the Direct Object of the verb demand.
The gist is that to get to the next level you need to grow your talents. If you keep performing at the same level then you'll be stuck at your current level.
The reason for the "your" and "you" is so that the message would apply to any person. So to apply to me, Max:
Every next level of Max's life will demand a different Max.