Didn't the pipe come with jetting information?
If not, then shame on the manufacturer!
If so, then follow it - they know best - even better than the know-it-all's here :p
If there weren't instructions, I'd call the mfr to double-check.
Some systems don't require re-jetting. Especially for the 426, where no pipe makes a noticeable power difference over the stock system (no more power = no jetting changes).
They may want you to change something though, if the pipe makes power in a different area than the stock system did.