I am not quite sure of what you are asking but here is something that I think is functionally equivalent to what you are showing doing: 
$text =~ s/(^|\s)"(?=\w)/$1“/gs;

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In short I am just changing the variable length lookbehind assertion and making it a regular captured pattern and putting it back after the match.

HTH

-enlil

In reply to Re: Match whitespace or start-of-string with lookbehind by Enlil
in thread Match whitespace or start-of-string with lookbehind by BigLug

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