Well... one thing you could do, is when your data has a specific format — and it looks like it does, judging by your example, that everything contains an "=" sign — is add a special hash key for your normal values. I'd propose a '$', reminescent of the string suffix in BASIC, or the scalar sigil in Perl if you like.

$href->{'p=root'}{'cp=1'}{'$'} = 'entry1';
$href->{'p=root'}{'cp=1'}{'n=1'}{'$'} = 'entry11';
$href->{'p=root'}{'cp=1'}{'n=1'}{'n=1'}{'$'} ='entry111';
$href->{'p=root'}{'cp=1'}{'n=1'}{'n=1'}{'n=1'}{'$'} ='entry1111';
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That should work well, without a conflict.

If you need more kinds of (meta-)data, you can add more special keys.