1) Please edit that post above...either remove the code or encase it in code tags required by forum rules (example in my signature)

2) I noticed I create a variable and forgot use it, so a final correction might be this:
If UCase(Trim(Cells(Rw, "A"))) = MyKey Then MyChn = Cells(Rw, "B") & "_"
If IsNumeric(Cells(Rw, "A")) And Cells(Rw, "A") > 0 Then Cells(Rw, "A") = MyChn & Cells(Rw, "A")