Why can't you just fly to SIN and then arrange the reticketing there? There would be a $125 re-routing charge, and increase in SIN taxes, and that's all. No repricing once you have taken the first segment. Also no "no show fee" if the ticket is nearly a year old (if I recall correctly that fee was only introduced a few months ago). The terms that apply to your ticket are the ones in force at the time you bought it, not the ones in force now.