It's more about the idea that I'm already in a program - will admissions committees see it badly, (as in everyone else who's applying doesn't have a seat and "needs" it more) or is it more that "wow, he's trying to apply to our school despite already being in med school!"
Not sure how admissions committees think. It's not necessarily about the DO guarantee. Would it be something that I should take off my resume when applying?
Yes. You don't submit a resume when applying. You submit an application and transcripts. Unless your transcript has a notation that you are in the program, there is no way schools will know, unless you tell them. And, even if it does, schools won't see it until the end of the cycle, since AMCAS verifies all your classes on your transcript but does not automatically pass the transcript on to the schools, although I think schools could access it if they want to.
MD adcoms will understand why you would want to upgrade from DO, so they won't hold it against you. But they also won't be impressed, so it won't help. That's why you have nothing to gain by going there. DO adcoms absolutely will hold it against you, so I don't think you have any reason to tell them if you want a DO upgrade.
