the following:
        
        $input = [[5=>"richard=red"], [15=>"york=yellow"], [25=>"gave=green"], [30=>"battle=blue"], [35=>"in=indigo"], [40=>"vain=violet"]];
        array_splice($input, 2, 0, [[10=>"of=orange"]]);
        var_dump($input);

gives this:

array (size=7)
  0 => 
    array (size=1)
      5 => string 'richard=red' (length=11)
  1 => 
    array (size=1)
      15 => string 'york=yellow' (length=11)
  2 => 
    array (size=1)
      10 => string 'of=orange' (length=9)
  3 => 
    array (size=1)
      25 => string 'gave=green' (length=10)
  4 => 
    array (size=1)
      30 => string 'battle=blue' (length=11)
  5 => 
    array (size=1)
      35 => string 'in=indigo' (length=9)
  6 => 
    array (size=1)
      40 => string 'vain=violet' (length=11)