You can copy any list by:
Click inside the smartlist.
Select all songs with Command-a
Now copy with Command-c
Go to a new (or existing) playlist and click inside it
Paste your songs in with Command-v
Now you can edit as much as you'd like.
Of course, you could also just Play the smartlist. That will put it into Playing Now. You can edit playing now as much as you'd like. This works well for "on the fly" mixes. If you want something more permanent, then a real static playlist is probably the correct tool for the job.
Brian.