Say you have a popupmenu for a field called Status with 3 options: Pending, Approved, Rejected. Create a new field called Statusglobal. In the field options store it as a globally stored field. Put that field on your layout with the popupmenu and your 3 options. Then set your save button to copy the value from the Statusglobal field into your Status field. When you change the data in the popupmenu it only effects the global field until you take the additional step of pressing your save button.
Are you talking about a popup; or dropdown menu?
They are two different things.
A popup can have a save or cancel button placed on it and you can set it up to revert or commit.