Default settings are managed in System Settings as documented in the section System Settings. System settings may be overwritten at the item level via the items options tab, item selection, and any of the analytic pages.
In Requirement Planning, changes made in the options tab, they are immediately applied to the item. Changes that are made via the item selection page or any of the analytic pages are applied once a new requirement plan or supply plan is run. This is done to retain the settings applied to the item at the time of Requirement Plan generation.
When S&OP is enabled, the behavior of the options is modified with the addition of an Apply Mode
With the Apply Mode, the user has a choice to apply the change to either the requirement planning, S&OP, or both. When applied to only Requirement Planning it is a temporary update. The setting is applied until the approval of the next S&OP plan. When the S&OP plan is approved, the settings made that were Requirement Planning only, are overwritten by the settings in S&OP.
For the setting to be applied in both areas at the same time, you should select Both from the drop down when saving. When choosing S&OP, the value will be applied to only S&OP and then to Requirement Planning when the S&OP is approved.