Dealer is feeding you shit. A slip on will not require a rejet on the 500
Hell, rejetting in general doesn't do jack for power on this bike: it's maxed from the factory.
2008 klx450r SM | Warp 9 | Pilot Power | Acerbis | Vapor | Pro Circuit
2012 zx-6r -- SOLD
2009 klx250sf -- SOLD
2008 zx-6r -- RIP 8/4/11
2001 ex-500 -- SOLD