boost thru MAFS

is it safe to do this, and if it is to what pressure?

You mean a GM Maf w/ translator or blowing through the stock mas? The stock mas will crumble at around 25 psi but you really shouldn't blow through the mas anyway since it was designed to be sucked through and you'll probably throw codes(although some people do blow through and have no problems). The GM Maf w/ translator can be blown through with no problems I believe although I don't know anything else about them since I don't use one.