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”