How to append a Value in cck field in a for loop?
Solved It by using 

$mynode = node_load(6); //Load the node before for loop
for($i = 1; $i&lt;=5; $i++) {
    $myprevious = $mynode-&gt;field_progress[0]['value'];
    drupal_set_message("My Previous".$myprevious);
    $mynode-&gt;field_progress[0]['value'] = $myprevious." ".$i." ";
    node_submit($mynode);
    node_save($mynode);
}
drupal_set_message("My Value".$mynode-&gt;field_progress[0]['value']);
$myprevous_progress = $mynode-&gt;field_progress[0]['value'];
$mynode-&gt;field_progress[0]['value'] = $myprevous_progress.' end.'.$myprevous_progress;
node_save($mynode);