Which model bike are you talking about?
I have a new 2020 and I have an Akrapovic Evo header to put on when it is derestricted, I also have the Moto GP short can, there are no 'not for highway use' stickers on the exhaust, there was a little red sticker in the packaging but I binned that immediately.
It will be loud, 112Db apparently, but mine is mainly for Euro track use, I will get a quieter can for UK days.
My understanding is the the Gen 4 will not actually 'need' mapping due to it using wideband O2 sensors and running in closed loop all the time, it essentially self adjusts the fuelling dynamically.
I expect I will get the ECU flashed when the developers get their stage 2 code sorted.