You cannot truly change your personality

I think as a 19 year old and you can correct me if im wrong ,but what I've learned from being alive so far is that you cannot truly change your personality without it affecting you in a negative way. It sucks because it means its way harder to get girls and what not but you cannot just put up a facade and just act differently without being miserable thats what I did and it for a long time and it was exhausting. I always hate when people say you just need a good personality to get girls but you literally can't change it passed early childhood.