Coming back to a tough subject after long break I'm returning to college next semester after about 5 years of a break from school. I took Calculus AB about 6-7 years ago in high school and will be taking BC next semester, which I need to transfer for Computer science.

In this case, I don't feel that retaking AB would be particularly helpful because I'm rusty on that content as well, and if I'm being honest here, it just doesn't fit with my transfer timeline.

My question is - how can I effectively come back to a difficult subject after a long break of not working with the materials?
I was in exactly your situation once.  I brushed up on Calculus I, which was basically about differentiation, on my own a bit, and signed up for Calculus II, which was basically about sequences, series and integration.  The Calculus II teacher helped me and it worked out fine.

Returning students often have several important things going for them: motivation, focus, self-awareness, impatience with some of the *$5%! that younger people will take lying down.

However, I don't know if the route I took would work for everyone.  Why don't you try some review of the material in your high school course, and see how you feel?  Do not hesitate to visit any math tutoring center within reach.  No one will check your credentials at the door.

Basic calculus courses are often offered in winter terms and summer sessions.  So you might not need to feel too constrained by your planned transfer timeline.