Styling different fields before/while rendering it using drupal_render I developed a custom module, in which I display tabs of different nodes. I render each nodes using the below piece of code,

$node = node_load($myNodeId);
$view = node_view($node, 'full');
$rendered = drupal_render($view);
print_r($rendered);


Is there a way in which I can access and style the individual elements in the $node, so that my $rendered contains the HTML that has the fields styled as per my wish.

Also a greedy thought, does drupal allow a call back function to be registered while rendering fields? so that my function takes care of rendering my fields of interest.
Yes, assuming I understand correctly that you would like the nodes presented in these tabs to be styled differently to nodes presented normally on the site then I would recommend the first thing you do is set up a separate "view mode" (ie. like "Full content" or "teaser") for this purpose. You can set set up new view mode using hook_entity_info_alter(), Entity view modes or Display Suite. For more information see this tutorial.

Once you have your new view mode in place, you should be able to replace the word "full" in your snippet with the machine name of the view mode. Then you will be able to do some themeing just by changing the formatter settings for your fields in your node type's display settings.

Their are many options for further overriding the themeing of the fields, you could for instance add the following code:

/**
 * Implements hook_preprocess_field().
 */
function MYTHEME_preprocess_field(&amp;$vars) {
  $vars['theme_hook_suggestions'][] = 'field__' . $vars['element']['#field_name'] . '__' . $vars['element']['#bundle'] . '__' . $vars['element']['#view_mode'];
}


...to your theme. This will allow you to create a theme function called something like MYTHEME_field__FIELDNAME__NODETYPE__VIEWMODE() (replace the uppercase words with whatever's relevant in your case).  This will override the funcion theme_field() and you will be able to customise as much as you like.