Sometimes just adding a new belief is all you need. So I would just use side be.
When I know that I have a powerful belief that is working against me ... Call it the I can'ts because... then I would first use part A because that is a belief that obviously needs changing.
For a belief "people don't like me" well it's not really a false belief, there probably are some people who don't like me. I'd save myself the time and go to straight to part B.
If I am saying, nobody ever likes me, because I'm no good. Side A... It means I have an all or nothing belief playing out that is definitely not helping me and needs changing. If I'm saying, 'some people don't like me because', then it's possibly true and I can easily work with just side B to develop the belief , people do like me and I can have a good relationship with them. Focusing on the why I want the belief, 'that people like me... because I am a good person.' for example.
If the belief you are working with will still be true sometimes. Don't try changing it. Work on adopting the belief that would serve you better.
If the belief has an all or nothing power to it. Then it needs changing first.
Even if you listen to side B first and discover your desired belief isn't taking hold because you have some as yet unidentified beliefs running in the background. You can always come back to Part A to work them through when you find them.
Alex