c:\@Work\Perl>perl -wMstrict -le
"use 5.010;
 ;;
 my $s = qq{xxx \@B grab \n this \@E yy zzzz \@B and \n this \n too \@E qq};
 print qq{[[$s]]};
 ;;
 my $start = qr{ \@B }xms;
 my $stop  = qr{ \@E }xms;
 ;;
 my $replace = [ 'ZOT', 'ZONK' ];
 ;;
 my $i = 0;
 $s =~ s{ $start \K .*? (?= $stop) }
        { $replace->[ $i++ % @$replace ] }xmsg;
 print qq{<<$s>>};
"
[[xxx @B grab
 this @E yy zzzz @B and
 this
 too @E qq]]
<<xxx @B ZOT @E yy zzzz @B ZONK @E qq>>