You'll be fine to negotiate; don't be afraid that it'll sour your relationship with the school. I do not think offers can be retracted simply because you're "negotiating" or "asking" for a better financial situation.
However, keep in mind that most schools will not change their scholarship status simply because you got scholarship from another school. The top schools, especially, won't change much. One way of understanding the scholarship situation is that each school acts on different basis for scholarship awards and that the schools must have seen something in you that's unique or "better" than other admitted students to offer you scholarship. This "uniqueness" from one school doesn't translate to another school in a similar fashion. For example, school A may be lacking your specific type of work experience, so therefore, in order to attract you to attending school A, a scholarship was provided. Let's say that school B has enough of your type and that school B isn't worry about you not attending because of the fact that there's enough of your type, just by telling school B that you've received scholarship from school A won't change B's basis for not offering you a scholarship. This reason carries throughout the top b-schools and while I'm always up for more money, just know that the chances are slim to get money from a no-money status.
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