How actually difficult is it? How much does new technology make it easier? New technology such as molecular nanotechnology will clearly provide a leap in the level of control over biology. Advances in biotech alone are changing the situation. It is clearly not getting harder or more expensive.
Fear, emotions and behavior have biological and chemical basis. Change and control those factors and you can effect behavior. Steroid rage is an unintended byproduct. LSD, heroin and other drugs effect behavior and perception.
If you were trying to cause a particular change, it seems reasonable that you could.