I am also struggling with bad habits. I guess it really depends on the habit, but the closest thing I've found to a 'hack' is not really a hack - it's the same

I am also struggling with bad habits. I guess it really depends on the habit, but the closest thing I've found to a 'hack' is not really a hack - it's the same concept that drug rehab centers use to get people off of addictive substances. That concept is complete removal or isolation from the bad habit, and surrounding yourself with people, so that you would feel shame if you continued the bad habit around those people. During this 'social' confinement period, you realize that you didn't need to do that bad habit in the first place. Obviously it would be sort of difficult to apply this concept with nail biting, but to give you an example, I really struggle with eating food in the middle of the night. So what I noticed was, after I took a week-long vacation to another country with family, and due to hotel circumstances, had to share the same hotel room, I stopped eating in the middle of the night (wouldn't want family to see me gorging on shit while they are trying to sleep at 1:00 AM and suffer the shame of that). For 7 days I did that, and it was just long enough to come back home and continue that momentum, because after day 5 I started wondering why it was so hard to stop doing that in the first place.