that is simple.
just change the vb setting in this line.
:sout=#transcode{vcodec=WMV2,vb=284,scale=0.5,acodec=mp3,ab=64,channels=2,deinterlace,croptop=2}:duplicate{dst=std{access=mmsh,mux=asfh,dst=localip:port}}
atm its set to 284kbps.
change it to whatever you require and it will stick to that.