Another way is to use the third argument of split to attack the string from both ends to isolate the element in double quotes.

knoppix@Microknoppix:~$ perl -E '
> $l = q{w,ww,"a,bb,ccc,3 ,ee,",4};
> @flds = split m{,}, $l, 3;
> push @flds, reverse
>    map { scalar reverse $_ }
>    split m{,}, reverse( pop @flds ), 2;
> $flds[ 2 ] =~ s{,}{-}g;
> $l = join q{,}, @flds;
> say $l;'
w,ww,"a-bb-ccc-3 -ee-",4
knoppix@Microknoppix:~$
[download]

I hope this is of interest.