title: arrayformula that can "skip" rows
body: <p>I need to introduce functionality into a google spreadsheet that will allow the user to edit the result of an array formula. The reason for the requirement is that an ARRAYFORMULA sets a default value for a group of cells, but the user sometimes needs to overwite these defaults. I'd like to know if this is even remotely possible.</p>
  
  <p>example:</p>
  
  <pre><code>Row(#)|Array_1 |Array_2
  ------------------------------------
   1    |a       |=arrayformula(Array_1)
   2    |b       |""
   3    |c       |""
   4    |d       |""
  </code></pre>
  
  <p>So all rows in Array_2 are populated by an array formula. However the user wants to go directly to the second cell in Array_2 and change its value. Of course, by design ARRAYFORMULA will break. Is there some way to modify ARRAYFORMULA, so that it will simply skip over the cell that the user has edited and continue on its way as if nothing has happeded?</p>