You should continue using the same registration code that was initially provided to you. If you no longer have the email with your registration code and are registered on the PokerTracker website you can view your code directly on the site under My Account -> Registration Codes.
Your PT4 registration code is good for use on two separate computers at the same time. You should use the same code on both of your computers. If you purchase a new computer, completely uninstall PokerTracker 4 from your old computer. You can then install PT4 on your new computer and continue using the same PT4 registration code that was initially provided to you and is located directly on the PokerTracker website under My Account -> Registration Codes. There is no need for a new code.
When PokerTracker 4 was initially released, we worked with 888, in order to provide HUD support on SNAP tables. 888 wrote a specific file to your computer, in order for us to provide a HUD on SNAP tournament tables.
Unfortunately, sometime during 2016, 888 updated their software and the file, we worked with them to create and is needed in order for us to support a SNAP HUD, was no longer being written. After numerous attempts of contacting 888 and six-plus months without hearing a response from them, we took the lack of response to mean that they deliberately removed the file so that no HUDs could be displayed on SNAP tables. Therefore, in early 2017, we removed all references from our site mentioning that PokerTracker supports SNAP tables.
If or when 888 changes their mind and starts writing the file again, the SNAP HUD should automatically work.