The only way one can justify breaking the ED agreement is if the alternative costs significantly less to attend. Without any aid, Michigan costs roughly $8k/year less than CMU. That’s $30k over 4 years, which is not negligible, especially if that amount will be taken out in loans.
However, if 12345hello123 has a better FA package from CMU, and difference in the cost of attendance is narrowed, I do not think turning CMU down is justified.