my ($bool,$lineno);
my $plus = 10; # mich interessiert die 10. Zeile nachdem $tmp
my $tmp = 'Transaction Project=9000';

while( my $line = <FILEHANDLE> ){
    next if $bool and $. != $lineno + $plus;

    if( $line =~/$tmp/ ){
        $bool = 1;
        $lineno = $.;
        next;
    }

    # mach was mit der Zeile x + 10...
}