#!/usr/bin/perl -w
use strict;
use warnings;
use Data::Dumper;

# original hash
my $h = {
 mm => 'July',
 yyyy => '1975',
 dd => '31',
 name => 'Milo',
 last_name => 'Manara',
};

print Dumper($h);

my $x = { mm=>'month', dd=>'day', yyyy=>'year' };
my $t;

@$t{map{$$x{$_}||$_}keys %$h) = values %$h;

print Dumper($t);