You will always have one set personality but it often changes because of hormones or experiences in life, for instance, if you are a 16 year old in high school like I am, your personality will probably change once a month, every human has 17 different emotions, unless you're a sociopath, but since you're wondering about this you probably aren't. Being that we all have at least 17 different emotions it is highly unlikely that we can completely control our personality 100%.
Etan