You've got a small typo--should be "(\d" instead of "\(d". One other thing with the solutions--they replace all varchars on the line with texts if any of them have over 255 characters. That may not be a problem depending on how things are broken up, but it's something to notice.

CREATE TABLE varchar (15) LastName, varchar (300) Notes
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(Apologies if my SQL is off, it's been a long time.) So here's just one more way to do it:

$buffer =~ s/varchar\s*\(
    (?: \d{4,}
      | 2 (?: 5 [6-9] \d*
            | [6-9] \d+
          )
      | [3-9]\d{2,}
    )\)/TEXT/gix;
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