Dim stolb, dlina, kolvo As Integer
Dim str1, str2, str3, slovo As String

stolb =  10 
slovo = Chr( 10 )

For i =  1  To ActiveCell.SpecialCells(xlLastCell).Row
str1 = ""
str2 = ""
str3 = ""

dlina = Len(Cells(i,  1 ).Value)
kolvo = Fix(dlina / stolb)
'---------------------------------------------------
If Len(Cells(i,  1 ).Value) > stolb Then
str1 = Mid(Cells(i,  1 ).Value,  1 , stolb) & slovo
End If
'---------------------------------------------------
For j =  1  To kolvo -  1 
str2 = str2 & Mid(Cells(i,  1 ).Value, stolb * j +  1 , stolb) & slovo
Next j
'---------------------------------------------------
If dlina > stolb And dlina Mod stolb <>  0  Then
str3 = Mid(Cells(i,  1 ).Value, kolvo * stolb +  1 )
End If
'---------------------------------------------------

Cells(i,  2 ).Value = str1 & str2 & str3
   
Next i