I don't see the problem.

use strict;
use warnings;

use Data::Dumper qw( Dumper );

$Data::Dumper::Useqq  = 1;
$Data::Dumper::Terse  = 1;
$Data::Dumper::Indent = 0;

my $s = chr(0xC9);
utf8::downgrade($s);
print(Dumper(unpack('H*', $s)), "\n");
utf8::upgrade($s);
print(Dumper(unpack('H*', $s)), "\n");

print(Dumper(unpack('H*', "\x{C9}\x{2660}")), "\n");
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5.10.0:

"c9"        # Ok
"c9"        # Ok
Character in 'H' format wrapped in unpack at 750077.pl line 16.
"c960"      # GIGO
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The internal representation is and should be irrelevant.

If you want to see the internal representation, it stands to reason that you should have to explicitely fetch it.