For new-twitter we have 2 (two) questions (all asked back in 2010), 1 (one) follower to it and... we have "new" Twitter working like a charm for past three years.
In this case just retag the questions. The new-twitter tag will then just disappear from the system.
If there were 10's or even 100's of questions with the tag I'd create a synonym, but for such a low number it's not worth it. Even as a low rep user you can suggest the edits and when they get accepted you'll get some more reputation.