How to change value in Excel drop down list

Solution 1:

As i mentioned in the comments, the only way to do this would be with VBA.

Here is one option. I've added comments throughout the code. This assumes that you are using a named range for the validation list named "List" and that it is on the same sheet as the cells being validated.

Option Explicit

Private Sub Worksheet_Change(ByVal Target As Range)

    Dim cell As Range
    Dim isect As Range
    Dim vOldValue As Variant, vNewValue As Variant


    Set isect = Application.Intersect(Target, ThisWorkbook.Names("List").RefersToRange)
    If Not isect Is Nothing Then
        ' Get previous value of this cell
        Application.EnableEvents = False
        With Target
            vNewValue = .Value
            Application.Undo
            vOldValue = .Value
            .Value = vNewValue
        End With

        ' For every cell with validation
        For Each cell In Me.UsedRange.SpecialCells(xlCellTypeAllValidation)
            With cell
                ' If it has list validation AND the validation formula matches AND the value is the old value
                If .Validation.Type = 3 And .Validation.Formula1 = "=List" And .Value = vOldValue Then
                    ' Change the cell value
                    cell.Value = vNewValue
                End If
            End With
        Next cell
        Application.EnableEvents = True
    End If
End Sub

You can also download the example spreadsheet I put together to test this out. (Contains macros!)