Is it permissible for someone who adheres to the Hanbali school of thought to adopt rulings from other schools of thought that are easier for him, out of fear of obsessive doubts (waswas), and is this considered blameworthy seeking of dispensations (tatabbu' al-rukhas)?

There is no harm for someone afflicted with obsessive-compulsive disorder (waswās) in adopting the easiest and most lenient of scholarly opinions. This is not considered blameworthy pursuit of concessions, but rather a permissible concession due to necessity. Obsessive-compulsive disorder is among the worst afflictions, so there is no harm for someone with waswās to act upon the easier opinion until Allah grants them recovery. However, in normal circumstances, the principle is that a person should seek a fatwa from someone they trust in their knowledge and piety when faced with differing opinions.