I've read taxes are based on state of residency as well. Course, someone can change that on their account, but don't be surprised if that comes back to bite you later.
In terms of the EAP software, even if the activation is OTA, the software is still present when you purchase it. Even if Tesla completely separated it from the safety systems software, and sent it over the net to the car after purchase, my guess is it would still be taxed because it doesn't appear to be a prewritten program as defined by law, which is a distinct product offered for general or repeated sale or lease.
Regulation 1502
(9) PREWRITTEN PROGRAM. A program held or existing for general or repeated sale or lease. The term also includes a program developed for in-house use which is subsequently offered for sale or lease as a product.
If at some point, Tesla starts selling EAP v13.8.1 for BMW, Ford, GM, and Tesla vehicles 2021 and newer, and you as a user can download and install said software on whatever you want, then that might not be taxed.