When you turn the cash requirement option to yes and restart the Fund Module, the cash requirement field turns editable.
However, modifying the value in this field only changes the cash requirement value in the fund table.
When calculating spending policy, the value used for displaying in the reports or used in creating the journal entries is the value found in the fundsummaryhistory record for the year, not the value in the fund table. Thus, changing the value manually on the screen will not impact the spending policy calculation, the reports or the journal entries created.
When spending policy is calculated and the create spending policy menu item is clicked, the value in the report is copied to both the fundsummaryhistory record and the fund record. Since the changed value doesn't update the fundsummaryhistory record, we typically leave the field uneditable (grayed out) so that there is no confusion and the values in the two tables remain the same.