I have one and also replaced the center insert. My original insert came with a plastic tube that ran from the outer shell of the target into the insert. I assume this was to help hold it in place. I couldn’t figure out how to install it in the new insert, so I gave up. The new insert slides backwards after many shots, and I occasionally push it back in so it is flush. My insert fits tightly enough that it isn't a real big issue, but it is annoying that a supposedly top notch target doesn't have a better way of switching out an insert.
I'm not bothered by the brightness of the paint, but if I were I’ll bet I could sand down the paint until it was dull.