Default Thread Subscription

To set the default thread subscription:

ACP -> Templates & Styles -> Templates -> Your Theme -> Member Templates -> member_register

Find:

<select name="subscriptionmethod" id="subscriptionmethod">
<option value="0" {$no_subscribe_selected}>{$lang->no_auto_subscribe}</option>
<option value="1" {$no_email_subscribe_selected}>{$lang->no_email_subscribe}</option>
<option value="2" {$instant_email_subscribe_selected}>{$lang->instant_email_subscribe}</option>
</select>

Replace With:

<select name="subscriptionmethod" id="subscriptionmethod">
<option value="2" {$instant_email_subscribe_selected}>{$lang->instant_email_subscribe}</option>
<option value="1" {$no_email_subscribe_selected}>{$lang->no_email_subscribe}</option>
<option value="0" {$no_subscribe_selected}>{$lang->no_auto_subscribe}</option> 
</select>

This only changes it for new members – by changing their default settings. Existing members will have whatever they made it in their preferences.