D7 - Can't set selected value of a webform select element
You can set value by using #value

$vars['form']['submitted']['country']['#value'] = 'BARBADOS';


But make sure that the select option key should be same

Example:

&lt;option value="BARBADOS"&gt;BARBADOS&lt;/option&gt;
$vars['form']['submitted']['country']['#value'] = 'BARBADOS'; //will work

&lt;option value="barbados"&gt;BARBADOS&lt;/option&gt;
$vars['form']['submitted']['country']['#value'] = 'BARBADOS'; //will not work
$vars['form']['submitted']['country']['#value'] = 'barbados'; //will work