If all parties in the promise are alright with it, all power to them. I don't think promises are anything meant to be so contractual. If they want to edit the promise go ahead. If you can't fufill the promise, tell them and figure it out. Staying 100% to your word is outdated imo. Communicate about your promises and agreements if issues or different ideas come up.
Life would be easier if people just communicated madami and were madami transparent to be honest XD