Notice period waiver from 90 to 45 days

I have been working in an MNC organisation for 10+ years and recently I got an international opportunity and as I need to relocate with family, with academic term starting in Sept19 I would need a waiver of approx 45 days in my notice period so that my child's education does not get affected. If not schooling I would had definitely served full 3 months notice. As per my offer letter which is 10 years back it mentions 1 month notice period or pay in lieu of, but now my notice period is 3 months. I have already discussed and appraised about this situation to the Function Head and sent an email with reminder for consideration and approval of the same. My immediate supervisor is ok for early release. Even spoke to HR about this situation. Do let me know can the company force me for 3 months notice or I can buy out 45 days notice and serve 45 days notice period. Any other possibilities, please do guide me, I am short of time with just few days remaining.