Edit|replace won't work (as you've seen).
You could use a macro, though:
Saved from a previous post:
Option Explicit
Option Compare Text
Sub testme()
    Application.ScreenUpdating = False
    Dim myWords As Variant
    Dim myRng As Range
    Dim foundCell As Range
    Dim iCtr As Long 'word counter
    Dim cCtr As Long 'character counter
    Dim FirstAddress As String
    Dim AllFoundCells As Range
    Dim myCell As Range
    'add other words here
    myWords = Array("widgets", "assemblies", "another", "word", "here")
    Set myRng = Selection
    On Error Resume Next
    Set myRng = Intersect(myRng, _
                  myRng.Cells.SpecialCells(xlCellTypeConstants, xlTextValues))
    On Error GoTo 0
    If myRng Is Nothing Then
        MsgBox "Please choose a range that contains text constants!"
        Exit Sub
    End If
    For iCtr = LBound(myWords) To UBound(myWords)
        FirstAddress = ""
        Set foundCell = Nothing
        With myRng
            Set foundCell = .Find(what:=myWords(iCtr), _
                                LookIn:=xlValues, lookat:=xlPart, _
                                after:=.Cells(1))
            If foundCell Is Nothing Then
                MsgBox myWords(iCtr) & " wasn't found!"
            Else
                Set AllFoundCells = foundCell
                FirstAddress = foundCell.Address
                Do
                    If AllFoundCells Is Nothing Then
                        Set AllFoundCells = foundCell
                    Else
                        Set AllFoundCells = Union(foundCell, AllFoundCells)
                    End If
                    Set foundCell = .FindNext(foundCell)
                Loop While Not foundCell Is Nothing _
                    And foundCell.Address <> FirstAddress
            End If
        End With
        If AllFoundCells Is Nothing Then
            'do nothing
        Else
            For Each myCell In AllFoundCells.Cells
                For cCtr = 1 To Len(myCell.Value)
                    If Mid(myCell.Value, cCtr, Len(myWords(iCtr))) _
                              = myWords(iCtr) Then
                        With myCell.Characters(Start:=cCtr, _
                                  Length:=Len(myWords(iCtr)))
                            .Font.ColorIndex = 3
                            .Font.Bold = True
                        End With
                    End If
                Next cCtr
            Next myCell
        End If
    Next iCtr
    Application.ScreenUpdating = True
End Sub
If you're new to macros, you may want to read David McRitchie's intro at:
http://www.mvps.org/dmcritchie/excel/getstarted.htm
This portion:
                        With myCell.Characters(Start:=cCtr, _
                                  Length:=Len(myWords(iCtr)))
                            .Font.ColorIndex = 3
                            .Font.Bold = True
                        End With
Changes the color and the boldness.
You may want to save first--so you can close without saving if you don't want to
keep the formatting changes.  Remember this kind of formatting only works on
text cells--not formulas--not numbers.