Sub PaulDemo()
Application.ScreenUpdating = False

Dim StrSty As String, StrRep As String, i As Long

StrSty = " Strong, Heading 1"

StrRep = "Placeholder1 ^& Placeholder2,Heading 1 ^& Heading2"

With ActiveDocument.Range.Find
  .ClearFormatting
  .Replacement.ClearFormatting
  .Forward = True
  .Format = True
  .Wrap = wdFindContinue
  .MatchWildcards = True
  For i = 0 To UBound(Split(StrSty, ","))
    .Style = Split(StrSty, ",")(i)
    .Replacement.Text = Split(StrRep, ",")(i)
    .Execute Replace:=wdReplaceAll
  Next
End With
Application.ScreenUpdating = True
End Sub