There is no patch, or custom 'system' folder. You just need an official Lineage 2 Interlude client and modify hostname resolving.
Modify hostname resolving
Edit C:\Windows\System32\drivers\etc\hosts (or /etc/hosts on Linux) and add below entries:
The whole file would look like this: [hosts file]
Accounts are created automatically. It means that it is created upon the first in-game login attempt.
If you want your account to be recoverable (in case of password loss), then use an email address as game login.
In order to reset password, contact admin via [email] or [forum]. New password will be sent to e-mail address used as account login.