Exhaust change?

I am planning on changing to a 4->1, and figured I would pick it up while I am the States, to save on shipping charges. The bike has the stock airbox, but with a K&N filter. Just curious if running this without jetting the carbs could cause any problems? I was planning on pulling the carbs anyway for a pre-season dust 'n clean when I get home. Am I better off to wait to install it until I can re-jet? Thanks in advance.

depends, my gpz 750 had a 4to1 and wolf pipe added new in 84. and the owner told me they never rejetted. plugs still the right color, and it gained in upper rpm range with no flat spots.

Yes, running without re-jetting can cause problems.
If it runs to lean, which is what a better breathing 4-into-1 exhaust will cause it to do, it can cause some real serious problems in the way of burnt valves, etc.

It also depends on the brand of exhaust system you plan on buying:
While Mac states "no jetting required" with their systems, all the other brands I've seen (V&H, Kerker, etc) do recommend re-jetting.

Best thing that I can suggest doing is mounting the exhaust up, slapping in a set of new spark plugs and then performing a plug-chop to see if it's running to lean/rich or just right.
Best results are achieved with a bike in a currently well tuned state.