Damn. That's a simple question that's hard to answer. I feel like a whole book could be written about this.
Depends on mine and that person's level of communication, trust and respect, and why the boundary was set up in the first place. Can we talk about what that boundary is, how big it is, and why it's there? Can we make choices that will allow us to take that boundary down? If yes, awesome, let's agree to work on things. If no, then I'm sorry there's pain involved, but it's either their pain for the boundary being up or my pain for it coming down. Some people are willing to work with you to make things work, some people not so much. Sometimes I'll make concessions for the sake of maintaining a relationship. Sometimes I just get burned, but you know what they say, "fool me once . . ."
I will say every person in my life is different and I'm an ever changing person with an ever changing life, and as a result every relationship in my life is different and my relationships are constantly changing. I will never not extend out a hand in good will, but the amount of good will I'm willing to offer might be very limited. Similarly, I will always be willing to give people the benefit of a doubt, to appreciate their ability to grow and change, but if I've been burned in the past, I'm not gonna just accept that someone has changed for the better without some good evidence.
Like I said, when I put a boundary up, there's a need for reflection and analysis, because they, myself, our relationship, and probably my relationships with others can all be affected.