Can I use the same concept on a hash value?

Yes. In exactly analogous fashion. Order the keys by value and then process your values in that order:

#!/usr/local/bin/perl
use strict;
use Data::Dump qw[ pp ];

my %pvalues = (
    1=> 0.5453980,
    2=> 0.4902384,
    3=> 0.8167950,
    4=> 0.2821822,
    5=> 0.4693030,
    6=> 0.6491767,
    7=> 0.9802138,
    8=> 0.1155778,
    9=> 0.9585124,
    10=> 0.4069490
);

my @orderedKeys = sort {
    $pvalues{ $b } <=> $pvalues{ $a }
} keys %pvalues;

my $d = my $n = values %pvalues;
$pvalues{ $_ } *= $n / $d-- for @orderedKeys;

pp \%pvalues;

__END__
c:\test>junk68
{
  1  => "0.908996666666667",
  2  => "0.9804768",
  3  => "1.02099375",
  4  => "1.410911",
  5  => "1.1732575",
  6  => "0.927395285714286",
  7  => "0.9802138",
  8  => "1.155778",
  9  => "1.06501377777778",
  10 => "1.35649666666667",
}
[download]

Of course, hash keys aren't intrinsically ordered, so you'll have to order them as needed for output, but one of the structure dumpers will do that for you.