First, if you ignore the email and not re-visit the topic, you don't get another one about the same topic/thread. The site will only email you once about a reply until you visit it again.
Second, you can manage your existing "subscriptions" in the User Control Panel...
ucp.php?i=main&mode=subscribed
Third, you can change your default for notifying you when you reply on a topic yourself (also in the User Control Panel)...
ucp.php?i=prefs&mode=post
Everytime you reply on a topic (or post), you can always specify the options for notification (changing your default for that thread).
Cheers... and Happy New Year!
-Alex