for (@Subscription) {
    Display_Subs(\%$_);
}
[download]

\%$_ says to take a reference to a hash $_ and de-reference it as a hash %$_ and then take a reference to that hash \%$_. Since you are not modifying that hash you could just do:

for (@Subscription) {
    Display_Subs($_);
}
[download]

sub List_Subscriptions {
    my (@Sub_ARRAY) = @{$_[0]};
#    my (@Sub_ARRAY) = @_;

    print "The Current Subscription List:\n\n";
    for (@Sub_ARRAY) { print " \t$_ \n"; }
    print "\n\n";
}
[download]

You are de-referencing the array (copying the whole array) when you could just use the reference:

sub List_Subscriptions {
    my ($Sub_ARRAY) = @_;
#    my (@Sub_ARRAY) = @_;

    print "The Current Subscription List:\n\n";
    for (@$Sub_ARRAY) { print " \t$_ \n"; }
    print "\n\n";
}
[download]