You want "not both preceded and followed by TOKEN", which is equivalent to "either not preceded by TOKEN, or not followed by TOKEN", and that we can do:

  my $split  = qr/
    (?<!$token) ,
  |
    , (?!$token)
  /x;

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Hugo

In reply to Re^3: Zero-width assertions fail with split by hv
in thread Zero-width assertions fail with split by Ovid

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