Assigning a hash to a registry key will only create additional subkeys/values for thoses keys of the right hand side hash, that aren't already a subkey of the left hand side registry key.

It will not lead to the deletion of subkeys in the left hand side registry key.

for deleting a subtree you have to get rid of its subkeys, so that delete can proceed.

Recursively traversing the tree, would do the job.

# this is only pseudo code
# refine and apply at your own risk (of damaging your Registry)

sub delkey {
   my $key = shift;
   delkey($_) for grep isasubkey($_), keys %$key;
   delete $key;
}
[download]

It's actually more difficult, since you have to make it delete $parent->{$keyname} as described in the docs.

Good luck!