I want to NOT have a two character patern in the middle part.

(?!re).
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is for regexps what

[^a]
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is for characters. So

(?(?!re).)*
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would restrict the presence of the regexp like

[^a]*
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would restrict the presence of characters where .* would otherwise be used.

You can combine this trick with the code in the example for (??{...}) in perlre (which handles nested parens).