In a debate, what's it called when you pretend to agree with a point you don't actually agree with, because you think it will make the person more open to agreeing with you on other points?
The title of the question is worded in a way that I will assume we already know the position of whoever we are debating.
If not, how could we else pretend to agree with their point?
So, we have two opposing views:
You know that I believe A to be true
I know that you believe B to be true
Then it is neither manipulative or in bad faith to "try on" the opposing view. How else can we learn more, if we are not open to understand or empathize? To answer your question, it's called being the devil's advocate:
a person who expresses a contentious opinion in order to provoke debate or test the strength of the opposing arguments.
"the interviewer will need to play devil's advocate, to put the other side's case forward"
I feel like devil's advocate is the opposite. It's taking the opposite stance you truly believe in order to debate someone you agree with. OP seems to be asking more specifically about taking a stance you don't agree with to argue against someone you disagree with.