So PPXII "dumped these restrictions entirely" and now the liturgy rules are based on personal preference of bishops and priests?
Well, yes, bishops have always been able to make certain accommodations regarding the Liturgy ... always. In some cases, even simple priest could dispense from various rules ... such as the Communion fast and Lenten fasting. And, in case you haven't noticed, the vast majority of Traditional priests are in fact
vagantes and are not under obedience to an ordinary. Some of Canon Law are hard-fast rules; others serve more as guidelines that the bishops, and sometimes even priests can dispense from.
Under normal circuмstances, a priest would have to get permission from his bishop to offer Mass at midnight on New Year's Day. I believe that such permission would readily be granted, but since there are no ordinaries to turn to, priests do have a little more latitude in this time of crisis.