#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?iu)#(?!(?:hashtag|DoNotRemoveThis)\b)[\w-]+(?=(?:\s+#[\w-]+)*\s*$)"
Local $sString = "Any #hashtag in the middle of the string should NOT be removed regardless of what it is, for example #DoNotRemoveThis #KeepThisHashtag and any hashtag at the end of the string should be removed UNLESS it matches the exeptions in the regex. #deletethis #DoNotRemoveThis #thismustgoaway"
Local $sSubst = ""
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