One-time settlement for son, and guardianship question

Dear all, My wife died during the divorce proceedings 3 months back. My 5-year-old son who was with my wife (at her father's residence), has been in the custody of maternal grandparents for the last 5 years. I've been paying maintenance of 11,000 per month (since 2017 - till date) as per a CrPC 125 order. Now (after my wife's death), the in-laws are asking me to do a 1-time settlement for my son, and asking me to assign them guardianship privileges. They want to change his name and surname also (replacing my initials with his mother's.) I've committed to giving 5 lacs as settlement now (although technically 1-time settlement won't apply for a father-son relationship). They're saying that they won't come back for money. My doubts are: If I give a one-time payment, will the existing CrPC 125 order stand canceled automatically? Or does this have to be canceled through the court separately? Secondly, can the guardian apply for revision of maintenance in the future when he wants? Are