How to grant edit access only to set of users defined in a cck field of a node?
As per me the best way to restrict the edit access would be by implementing hook_node_access, something like the following:

function MODULE_node_access($node, $op, $account) {
  if ($op == 'update' &amp;&amp; $node-&gt;type == 'YOUR_TYPE' &amp;&amp; $node-&gt;field_custom[LANGUAGE_NONE][0]['value'] == 'some value') {
    return NODE_ACCESS_ALLOW;
  }
  else {
    return NODE_ACCESS_DENY;
  }

}