Std Hours not updating in Basic comp

ORacle 9.2 - We have a default std hours per day in our company option but there are employees who have different std hours/day but same std hr/yr and std days /year. But JDE , doesn't allow us to update the std hr/day unless we delete and update the std hr/year. We cannot do that bec we need to cater for employees having 4 days (with different std hr/day) but still have the same numbers of hours (std hrs/year) with those employees doing it 5 days. How do we go about allowing these in our system?