Edit custom field using user_presave hook during account creation I have made a custom field for user field_custom_xyz from the admin GUI.
Now after i saved it i got two tables into the database : one for data and one for revisions.
I already have a huge database into which a lot of users are already there.

I have two questions : 


How can i make sure that i can assign default value to each user at the time of creation of this field?
Let's say if i have to assign a default value of 0 (or null in case i don't follow step 1).
how can i change that value at the time of new registration using  hook_user_presave ?


I want to override the default value of this field using user_presave hook in some custom module lets say 'abc' module

so far i have tried : 

$account-&gt;field_custom_abc['und'][0]['value'] = 0;

but that doesn't work, any suggestions.
thanks in advance.
Try this out:

/**
 * Implements hook_user_presave().
 */
function mymodule_user_presave(&amp;$edit, $account, $category) {
  $edit['field_custom_xyz'][LANGUAGE_NONE][0]['value'] = 0;
}