The sentence
If I were you, I wouldn't do this
One can add emphasis to the sentence, by saying
Were I you, I wouldn't do this
However, I noticed that in everyday English people tend not to use the subjunctive mood, but standard Simple Past tense.
If I was you, I wouldn't do this.
So, is it possible to say
Was I you, I wouldn't do this?
It looks a little bit strange for me.