Doctor's have the ability to test if an individual is genetically predisposed to a disease. a predisposition to a disease means that you may have a genetic link to a certain disease such as heart disease, diabetes, and cancer. if you were to have a genetic test, and the results were positive, meaning you are at high risk to develop a disease, what would you do differently? what changes would you make? why or why not?

Yes doctors can test the genetic predisposition of an individual to a disease but it is not done by genetic testing, unless they are chromosomal abnormalities or DNA sequencing abnormalities rather than just diseases with genetic predisposition such as malignancies. Heart disease, diabetes, and cancer; while does have a significant genetic predisposition, cannot be risk stratified by genetic tests because of (1) it is too costly and (2) it cannot be accurate. These genetic predisposition is best taken care of by doing proper history and physical examination as well as doing a family genogram. 

If history and physical examination revealed that you are high risk to develop a disease (i.e. heart disease) then you should be advised to have lifestyle modification as well as some maintenance medications, if warranted.