Here's another approach:

    $line= <<END;
10 PRINT "<29>This is dim.<30>EThis is reversed.<28>This is bold.<27>"
END
    my %fix= ( "<29>" => '@(-38)',
        "<28>" => '@(-40)', "<27>" => '@(-35)' );

    my $pattern = join("|", map "(?:$_)", keys %fix);
    1 while $line =~ s/("[^"]*) ($pattern) (.*?")/$1";$fix{$2};"$3/gx;
    $line =~ s/"";//g;
    $line =~ s/;""//g;
    print $line;
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