Take a look at Data::Rmap. Something like this should do the trick.

use Data::Rmap qw[ rmap_hash ];

rmap_hash{
    for my $key ( keys %{ $_ } ) {
        next unless $key eq 'Target key value';
        $_->{ $key } =~ $someRegex;
    }       
} $refToArbitraryStructure;
[download]

Whether that is an easier than what you have is your decision. More efficient? Benchmark it :)