I know that on another site that uses vBulletin 3.0.0, the

"Subscribe to this Thread" link (pointing to /subscription.php?do=addsubscription&t=X)

at the bottom of each thread automatically changes to

"Unsubscribe from this Thread" (pointing to /subscription.php?do=removesubscription&t=X)

if someone is already subscribed to that thread. Is there any way to implement the same functionality on FlyerTalk?