Yes, you can apply for a certificate at any time. (you have the correct number)
It only takes a couple of hours for Mota to remove you from the system and free up the tax allocation for your new car, make sure the dealer inputs it onto the system before you leave.
If the car is brand new then the dealer should be able to sort it. (if you have the new cert)
If not then you will have to go to a post office to change the tax class which will trigger a refund of the remaining months. (make sure the clerk doesn’t try to stamp the certificate as this now invalidates it for future use and you would have to call to get another certificate)