Is your personality different in relationships than in other contexts?

Usually yes. You might be extroverted at work but introverted at home. You might be controlling at work but accommodating in romance. Understanding your "relationship personality" (how you actually show up in partnership) helps you choose compatible partners and work on growth areas.

How is relationship personality different from MBTI?

MBTI measures thinking/feeling/processing style. Relationship personality measures how you function in partnership: Do you lead or follow? Do you pursue or withdraw? Do you give or receive? Two people with the same MBTI can have very different relationship personalities based on attachment history and learned patterns.

Can you change your relationship personality?

Yes, with awareness and effort. If you tend to pursue/chase, you can learn to lead. If you tend to withdraw, you can learn to engage. Therapy helps change ingrained patterns. But awareness comes first—the quiz reveals your default, then you choose whether to adjust it.