You just need to add a loop to select and process each sheet.
Code:
Sub ReplaceText()
For i = 1 To ActiveWorkbook.Sheets.Count
Sheets(i).Activate
Cells.Replace What:="Grand Total", Replacement:= _
"=""Grand""&REPLACE(A6,1,FIND("": "",A6)+0,"""")&"" Total""", LookAt:=xlPart _
, SearchOrder:=xlByRows, MatchCase:=False, SearchFormat:=False, _
ReplaceFormat:=True
End Sub
If (Range("A6") = "Contract Type: Firm Fixed Price") Then
Cells.Replace What:="Fee", Replacement:="Profit", LookAt:=xlPart, _
SearchOrder:=xlByRows, MatchCase:=False, SearchFormat:=False, _
ReplaceFormat:=False
End If
Next i
End Sub