Re-tune/flash necessary with full exhaust upgrade?

[Inline4_imp]

You know, I was worried about the same issues as you. I recently upgraded from a Yoshimura RS3 slip-on canister to a full Nojima 4-into-1 exhaust.
The bike had no issues with the Yoshi performance-wise, BUT I found it ran a tad rich. I could stick my finger in the exhaust outlet on the Yoshi and there was always a little black soot there. No biggie but I knew it wasn't quite right.
Since I've added the full Nojima, the bike runs crisper and cleaner..........
I have about 700 miles since the change and no soot what so ever...
Even though the exhaust note is a bit more subtle with the Nojima, the bike absolutely SCREAMS when you push it to the mid/upper rpm range, especially under load.
I do want to get a PCV or whatever its called and perhaps a reflash if needed just to get optimum horsepower from the engine, but as she is right now, I couldn't be happier nor could I smile any wider when I run it hard through the gears.