A hash slice and delete will do this handily, 

@{$href}{map {to_new($_)} keys %$href}  # wrong
    = delete @{$href}{keys %$href};

[download]
Since the values are all scalar hashrefs, this code doesn't care about their contents, and leaves them alone.

Update: Roger++ points out that the keys got clobbered. Mapping the new keys externally fixes that, 

my @newkeys = map {to_new($_)} keys %$href;
@{$href}{@newkeys} = delete @{$href}{keys %$href};

[download]

After Compline,
Zaxo

In reply to Re: altering HoH keys by Zaxo
in thread altering HoH keys by 3dbc

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