Can a person who was strict regarding the impurity of alcohol now adopt the view of its purity due to his obsessive doubts (waswasa) concerning everything he touches, his hand having alcohol on it, or his shaking hands with people who use alcoholic perfumes?

The issue of alcohol's impurity is a matter of disagreement among scholars, and the difference of opinion on it is permissible. Among those who favored the view of its purity is the esteemed scholar Ibn Uthaymeen. There is no blame on anyone who wishes to follow a scholar who issues a fatwa (definition) to this effect, as long as they are following a trustworthy scholar. For someone who suffers from obsessive doubts, it is permissible to adopt the easiest of opinions to alleviate hardship and دفعا للمشقة (remove difficulty).