I gave your third approach a try. I tried this:

   undef %hash
%hash = (%hash, split /X/ 'fooXbar');
%hash = (%hash, split /X/ 'bishXbash');
foreach(keys %hash) {
   print "3: $_ = $hash{$_}\n";
}
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It produced:

 bish = bash
 foo = bar
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