assign double click event for multiple cells - easier way?

Try...

Dim CostC As String
    If Selection.Count = 1 Then
    
    'BEGIN Cost Center Assignments
        If Not Intersect(Target, Range("C4:C42")) Is Nothing Then
            CostC = Target.Value + "_S"
            ThisWorkbook.Sheets(CostC).Visible = True
            ThisWorkbook.Sheets(CostC).Activate
        End If
    End If

Another option:
Place this macro in the code module for the "RevenueALL" sheet.

Private Sub Worksheet_BeforeDoubleClick(ByVal Target As Range, Cancel As Boolean)
    If Intersect(Target, Range("C4:C42")) Is Nothing Then Exit Sub
    Application.ScreenUpdating = False
    Sheets(Target.Value & "_S").Visible = True
    Sheets(Target.Value & "_S").Activate
    Application.ScreenUpdating = True
End Sub