as for the buttons, take a soldering iron and a desolder braid/solder suck bulb and suck that solder off the buttons. no risk to do so, just make sure you don't hold it too long there lest risking lifting the pad from the PCB
as for the rubber stoppers, i'm not so sure, what you can do and what some people have done is take kitchen cabinet liner, the grippy stuff that looks like a mesh of squares and glue that down to the back plate. People have had good results with that stuff and non-slip