Here's the general idea:
 Code:
; Define the Old and New words
$Old = Oldword
$New = Newword

; Enumerate the list of files.. either from a fixed list (shown below) or using the DIR command
$aFiles = 'File1', 'File2'
For Each $File in in $aFiles
  ; Load the file into an array. Use the FileIO() UDF
  $aData = FileIO($File, 'R')

  ; enumerate the file and replace any occurrence of the word
  For $Ptr = 0 to UBound($aData)
    $aData[$Ptr] = Join(Split($aData[$Ptr], $Old), $New)
  Next
Next
; Write the updated file back
$aData = FileIO($File, 'W', $aData)
Given, this is an EXAMPLE of how it could be done - you'll need to flesh it out with some error checking and possibly other logic to insure that only specific instances are replaced, but this shows how to enumerate a list of files, and then enumerate the contents of each file.

Glenn

PS - the latest FileIO UDF can be downloaded from my web site.
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Actually I am a Rocket Scientist! \:D