Thanks, folks, this is all very interesting. I also found that Lexical::Alias works for this.

use Lexical::Alias ('alias');
my $ref = { a => 'b', c => 'd' };
my %hash; alias %{$ref}, %hash;
print $ref->{'a'}; $hash{'a'} = 'e'; print $ref->{'a'};
[download]

Yields:

$ perl alias.pl
b
e
[download]

The funny ordering, which goes against the common syntax in shells for the alias statement, got to me the first time. Nevertheless, these non modular solutions were what I wanted to know about.

Cheers