Updating other modules schema when creating custom module
You should make use of the hook_schema_alter to update entity schema of existing schema's.

function YOURMODULE_schema_alter(&amp;$schema) {
  // Add field to existing schema.
  $schema['users']['fields']['timezone_id'] = array(
    'type' =&gt; 'int',
    'not null' =&gt; TRUE,
    'default' =&gt; 0,
    'description' =&gt; 'Per-user timezone configuration.',
  );
}