it's strange if I do the same code in a XLSX file, I have an error on accent.

XLSX files contain XML files, and assuming Excel is writing them correctly, these encoding issues should hopefully not arise. In other words, the strings you get should not need the extra decode step, and that line in my code could be changed to my $val = $sheet->{cell}[$c][$r];.

I would like to convert MacRoman in HTML é --> & eacute

As I said and as haj explained some more, this doesn't really make sense in the context of XML, only in HTML, but you haven't explained how you want to integrate the two. I think the best thing would be if you could show an example of exactly what the output file should look like. Note that even in HTML, if the encoding is declared correctly, you don't even need escapes like é.