I would create a user defined function
Function prep_lower(the_text)
Dim prep_list(10, 10)
prep_list(1, 1) = "As"
prep_list(1, 2) = "as"
prep_list(2, 1) = "Or"
prep_list(2, 2) = "or"
prep_list(3, 1) = "Is"
prep_list(3, 2) = "is"
'more items......
For n = 1 To UBound(prep_list, 1)
the_text = Application.WorksheetFunction.Substitute(the_text, Chr(32) & prep_list(n, 1) & Chr(32), Chr(32) & prep_list(n, 2) & Chr(32))
Next 'For n = 0 To...
prep_lower = the_text
End Function
then enter text in, say, cell a1 and the formula =prep_lower(A1)
in b1