I interpret your question as "how do i change the hash key in a hash?"

If you can change the original hash, I suggest this code snippet, which deletes entries with the non-utf8 keys and reuses the values for the utf8-version key.

for (keys %oldhash) {
    # change key and keep the value
    $oldhash{utf8_on($_)} = delete $oldhash{$_};
}
call_pyfunc(\%oldhash);
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