"if you not" sounds classic to me. nowadays, it is simplified by "if you don't".
anaway, "if" can either be replaced by "should", "had" or "were" just to sound a bit exciting and convincing.
if you have anyquestion = should you have any question
if not for this guy, the girl would've not been saved = were it not for this guy, the girl would've not been saved
if I knew it in the first place = had I known it in the first place...
back to your question, they are quite the same in meaning, it's just the style of saying/writing it.