[Carnage]

I've been looking at doing something similar myself. From my research into how the process works i'd suggest taking a look at class_paid_subscription.php.

line 338 contains a hook thats called once a user has completed payment for a subscription.

PHP Code:

    /**
    * Creates user subscription
    *
    * @param    int        The id of the subscription
    * @param    int        The subid of the subscription, this indicates the length
    * @param    int        The userid the subscription is to be applied to
    * @param    int        The start timestamp of the subscription
    * @param    int        The expiry timestamp of the subscription
    *
    */
    function build_user_subscription($subscriptionid, $subid, $userid, $regdate = 0, $expirydate = 0) 


Thats the method the hook appears in you would need to use $subscriptionid and possibly $subid in deciding what to do in your switch statement.

As a final note, try to use the vbulletin datamanagers for editing the users reputation as opposed to doing it manually.