perl -e"BEGIN{$/=\(1024**2)  }" 
-pe "s/\x00\x42\x00\x11/\x00\x42\x00\xf0/sg" infile >outfile1

perl -e"BEGIN{$/=\(1024**2-3)}" 
-pe "s/\x00\x42\x00\x11/\x00\x42\x00\xf0/sg" outfile1 >outfile2