array-walk-recursive.php

<?php
$data = array(
  'row1'  => array(
    'col1' => 'value1',
    'col2' => 'value2',
    'col3' => 'value3',
    'col4' => 'value4',
  ),
  'row2'  => array(
    'col1' => 'value1',
    'col2' => 'value2',
    'col3' => 'value3',
    'col4' => 'value4',
  ),
);
$prefix = 'foo';
array_walk_recursive($data, function(&$value) use ($prefix) {
    $value = $prefix  . '-' . rand() . '-' . $value;

});

print_r($data);

// Result will be 

Array
(
    [row1] => Array
        (
            [col1] => foo-808219862-value1
            [col2] => foo-1123986045-value2
            [col3] => foo-779885783-value3
            [col4] => foo-139808836-value4
        )

    [row2] => Array
        (
            [col1] => foo-864851992-value1
            [col2] => foo-1640224340-value2
            [col3] => foo-2018795883-value3
            [col4] => foo-422754453-value4
        )

)