Yes. I installed a decatted header and mufflers on my buddy's 2017 RGS. He does not have a tuner yet and says that his bike is a lot more responsive now. However, I suggested that he still get a tuner to balance out the air fuel ratio.
Be careful with your add-ons, the Magnuson-Moss warranty act does not apply to 2017’s and up. Programmers and header replacement will void your warranty. EPA vs. Harley court settlement forces Harley to void and blacklist your bike. If you don’t care, a simple cam replacement can get you as much as 110HP and 117lbs. of TQ. https://www.fuelmotousa.com/p-33193-dyno-charts.html