#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?m)^((?:(?:(?!")[^|\r\n]*|"[^"\r\n]*"(?=$|\|))(?:$|\|))*+)(")"
Local $sString = "123|110092|ACCT|"HC Account"|"Account1||||||||||||"Mary"|||"|"||||132|"STE|504"|1253|Unspecified Account|||N||ACTV|Active||||04/30/2013|12/31/2099|||||||||||||" & @CRLF & _
"123|110092|ACCT|"HC Account"|\"Account1||||||||||||"Mary"|||"|"||||132|"STE|504"|1253|Unspecified Account|||N||ACTV|Active||||04/30/2013|12/31/2099|||||||||||||" & @CRLF & _
"123|110092|ACCT|"HC Account"|"Account1||||||||||||"|Mary"|||"|"||||132|"STE|504"|1253|Unspecified Account|||N||ACTV|Active||||04/30/2013|12/31/2099|||||||||||||" & @CRLF & _
"123|110092|ACCT|"HC Account"|"Account1||||||||||||"Mary|"|||"|"||||132|"STE|504"|1253|Unspecified Account|||N||ACTV|Active||||04/30/2013|12/31/2099|||||||||||||"
Local $sSubst = "$1\\$2"
Local $sResult = StringRegExpReplace($sString, $sRegex, $sSubst)
MsgBox($MB_SYSTEMMODAL, "Result", $sResult)
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for AutoIt, please visit: https://www.autoitscript.com/autoit3/docs/functions/StringRegExp.htm