I take it off and use paint stripper. It's metal if IIRC. Nothing else has worked (fast enough) for me.
If you get an Angry Gun suppressor it'll come with a really nice fitting flashhider...so just unscrew the old one and screw on the new one.
So far as the stock goes...take a look at how the notches are...just copy them and file in another set where you want them. It's that simple....and there's a Youtube vid of it somewhere too.
If your break the front tab off the end cap you can just glue the cap back on permanently...mine was broken and I modded it with a lower M4 RIS...but because of the damage I had to glue on the end cap. Doesn't affect anything and all the innards come out from the back anyways.