There's no need to call yourself a "career changer" - just say you're changing your field of study. This can even work quite well for you, assuming you do well in the post-bac... there's a trend towards preferring well-rounded people who are not totally pre-med tunnel vision. You could claim that you intentionally used your undergrad years to pursue a passion, purely for personal enrichment, because you would never again have that opportunity, and you are now pursuing another, more practical passion (or something like that.)
When you're right out of college, you feel like one big chapter in your life is behind you. But when you get older (I'm 34) those younger years - 18 to, say, 25, 26, or 27, all sort of blend... that all seems like one chapter. From an older person's perspective, it doesn't look weird to have studied one thing and then move on to study something else. I don't think any older person, other than maybe someone who has had total tunnel vision, and never dabbled outside of one field, would think it was odd that you spent "4 whole years" studying one thing, and then switched to something else. I think it's even less difficult to explain when your major area in college was something like English (which really isn't easily applicable to a career.) It really does look more like a personal passion, you wanted to be a well-read person, etc., and it's not necessarily what you always thought you'd do for a living, or anything like that. No one would wonder how you could switch fields when you haven't even worked in the "English field" yet.
I digress, a bit, but I thought I'd give that opinion.
