Hello Grigoriy,
1. The Download ID will not change until you change your password or email address on our site. It is valid (as in: using it will allow you to download our Professional software) as long as you have an active subscription. When your subscription expires, it is no longer valid. When you renew your subscription it becomes valid again.
You can use it on as many sites as you want. The Download ID merely tells us that the guy who's requesting to download an update is you, so that we can check if you have a valid subscription before serving your update request. It is in no way bound to a domain name. In fact, I have no idea what are the domain names of your sites. I don't track this information.
2. Yes, that's correct!
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!