The stuff you mentioned
shouldn't VOID your warranty. As long as you're not modifying the engine or suspension, they won't say anything. They might give you a hard time with the exhaust tho. A lot of dealers will try to blame that "High Performance" part on something stupid and unrelated like your windshield wiper motor breaking

The easiest thing would be to ask the dealer.
I do have a suggestion... I wouldn't REPLACE any parts like taillights or exhaust because those are still covered. If something breaks, you have a free replacement. So why not get the most out of it?
The biggest tip I have for anybody starting out is WAIT and THINK about what you're buying. A lot of people buy neons, altezzas, and spoilers and then realize that the stuff looks "rice" and then they got to sell it for next to nothing. Tust me, I've seen it happen many times. So just be patient, look at some clean 01 civics on the net, then decide what you like and what you want to spend your cash on. Hell if you put together all the money from what you mentioned (spoiler, neons, altezzas) you could probably have enough to buy some nice rims or a suspension kit. That will make your car look muuuuuuch nicer than the stuff you mentioned. (IMO)
P.S. Check your PM