Change the text within a cell to the text within another cell and paste in another co

[snb]

sub M_snb()
  sn=sheets(1).cells(1).currentregion.resize(,3)

  for j=2 to ubound(sn)
    sn(j,2)=sn(j,3)
    if lcase(left(sn(j,1),3))="ext" then sn(j,2)=""
  next
  sheets(1).cells(1).currentregion.resize(,3)=sn

  for each it in sheets(1).cells(1).currentregion.columns(2).specialcells(4)
     it.offset(,1).copy it
  next
End Sub

[Rick Rothstein]

sub M_snb()
  sn=sheets(1).cells(1).currentregion.resize(,3)

  for j=2 to ubound(sn)
    sn(j,2)=sn(j,1)
    if lcase(left(sn(j,1),3))="ext" then sn(j,2)=""
  next
  sheets(1).cells(1).currentregion.resize(,3)=sn

  for each it in sheets(1).cells(1).currentregion.columns(2).specialcells(4)
     it.offset(,1).copy it
  next
End Sub

When I run your code, I just get Column C duplicated in Column B. I think the 3 that you had should be a 1 as shown in red above.

[Rick Rothstein]

Here is another macro that you can try (it runs quite quickly)...

Sub Test()
  Dim LastRow As Long
  LastRow = Cells(Rows.Count, "A").End(xlUp).Row
  Range("B2:B" & LastRow) = Evaluate(Replace("IF(LEFT(A2:A#,3)=""ext"",C2:C#,A2:A#)", "#", LastRow))
End Sub