How much do you identify with your type?
By that I mean, how much do you see your MBTI type as a true reflection of you?
It's parts of me, but I don't believe that any of us are 100% our type. We can't be; not one of us will line up completely with it because we're all individuals and not clones or robots.

Those who feel that they are 100% their type are probably forcing themselves into the MBTI box rather than exploring all of who they are.
Do you see it as integral to your personality, or just one of a million things that define you?
I was me before the MBTI, and I'll continue to be me with or without it. I like that there's something that let me know I wasn't completely crazy at times, and I liked having a system that helped map out much of my strengths and weaknesses, but I don't gauge my life by looking at the magical MBTI crystal ball and using it to guide my decisions. Sometimes I won't act like my type at all, and that's ok too. It doesn't make me any less me.
How important is your type on the hierarchy of "things that define you"?
Not very. See above.
Would it matter greatly if it turned out you weren't the type you believed you were?
Nope. I actually did all that soul-searching. INFJ wasn't my first choice, actually. I took an MBTI "official" test ages ago and ended up an INTJ, but as I investigated INTJ more in depth it didn't quite feel right. I tried it on for size and I matched with some of it, but then I dated one...and knew I wasn't an INTJ. Then I experimented with ISFJ for a bit, which seemed close as well...but I realized I wasn't after a few really, really bad job situations showed me that I was not detail oriented enough (and I was too long-term thinking and too slow) to keep the jobs I had.
Then my life kind of imploded for a few years and I went on the hunt (again) to find out who I was so I could make changes. I tried Ansir which worked for a while, but I was still unsure of different aspects. So I tried Enneagram. On one of those websites, I met another person who was a well-rounded, beautiful INFP and we shared similar interests, so I thought maybe I was an INFP. But she was the first to suggest that maybe I was an INFJ, and to explore the possibility. So I found another website that talked about INFJs, and joined a Yahoo INFJ webgroup, but something about it really irritated me (the group was a total drama fest and kept flooding my mailbox with tripe), so I left it.
But by process of elimination I slowly came back to INFJ. My decision wasn't arbitrary, and it was more of a decade long search for self. But I finally got to the point where I had to say, "yes. I'm an INFJ and I don't need to search anymore." Once I got to that point everything else sort of came together, and I didn't need to look at another type.
In truth I'm probably closest to an INFJ/TJ hybrid, but that slight "F" makes far more sense than the slight "T".
How would that change your perception of yourself?
Already did it.

I think the exploration helped me find myself, and be comfortable with myself as is.