Yes! No! Maybe! Or at least those are the signals coming out of Montreal...
Seriously though, he's not (yet?) the new closer. Tucker will still be the primary closer, but both he and Stewart will occasionally be used for two innings, or possibly more on rare occasions, in which case the other guy would close the next day.
If things stay the way they are now (ok, I admit I can't say that about Montreal's bullpen and keep a straight face
), I'd expect Stewart to pick up about a third of the Expos' save opportunities. I fTucker falters, however, it's Stewart all the way.