at least using standard billing schedule functionality it can't be done but what I have seen before is that there would be changes, co-term, add-ons etc. which I still will say is just bad practice to modify an approved order for - depending on size of business it may not be a big deal but it does break basic compliance rules, especially if any revenue is pro-rated but ultimately it is on Finance to yay or nay that - the custom record is of course a bigger thing to do