Well originally I started the second one (Hobbes) to start over before the offer and subsequent button were provided to nuke your stats/data.
After that point I was studying for the HSK basic exam so I tried to do a lot of reps with that vocab list and learn it quickly, which was work of a rewarding nature.
After the test date (at which point I didn't actually take the test--don't ask), I took about a week and a half off, killing my reviews (though of course there is "save me" etc.)
When I came back, I was doing the book list from Elementary Spoken Chinese along with my class and the dreaded 听写. So I wanted to focus on my list words and reviewing them primarily, letting my hsk list slide.
Long story short if there had been a way to insert the new list on my account, with a way to not just pause but always make sure that all other material/reviews came up after finishing my reviews from the new list, I could do the same thing with one account (some version of cram mode?). Granted, I realize this is a pretty special case and goes blatantly against the whole review when its ready, keep reviewing basically forever to get the long term memory benefits philosophy of SRS. Therefore I assume it would not effect most users, and might even hurt people (like me) who might do it out of laziness :)
Peace.