$text->{$line}[$pos - 1] = $word;
       ^ ^      ^
       | |      |
       | hash   |
dereference    array
[download]

I used $pos - 1 as positions start from 1, but array indices start from 0.

Note that the bracket types are the same as when creating the data:

$VAR1 = {
          'c3' => [
                    'Phasellus',
                    'non',
                    'erat'
                  ],
          'b2' => [
                    'consectetuer',
                    'adipiscing',
                    'elit.'
                  ],
          'a1' => [
                    'Lorem',
                    'ipsum',
                    'dolor',
                    'sit',
                    'amet,'
                  ]
        };
[download]

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]