Finally a definitive answer.
My understanding is that the accelerated battle pass is a different thing. So you will keep your accelerated battle pass token to be used in the future.
I thought maybe you could purchase the Premium Battle Pass separately. Although, the Ultimate Edition apparently comes with both the Premium Battle Pass version and the Accelerated Battle Pass version. This might be a miscommunication by the structure of the table and how the battle pass version purchases are handled.
I suppose we will have to wait for season 2 if purchasing the Premium Battle Pass replaces the Accelerated Battle Pass token or if it can be redeemed still in a later season. Very complicated stuff.