No you will not become a vampire by casting a spell on yourself. There is no way to become something you are not. It would be like saying I want to change my gender. You were born a vampire or you werent.
People may be telling you to use caution when working with black magic. The dark arts are very addictive and alluring to those who have not practiced them before. The dark arts also can come with a price, and it is you that will end up paying that price in the end. The consequences may not be immediate but they will appear soon or later. Prepare yourself and do your research first before practicing with the dark arts.
Yeah, EarthFire. Your right. Its kind of like in Full Metal Alchemist. That the two brothers tried to bring their mom back from the dead with alchemy and the younger brother lost his body and the older lost its leg. And then the older bro exchanged his right arm for his brother's soul to attach him to a suit of armor. Thats something similiar.