#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "((?:\<[^<>]+\>\s?)?)([:]\w+(?!\w*[;]))((?:\s?\<\/[^<>]+\>)?)((?:(?:.(?!\1\2\3))*.){2})\1\2\3"
Local $sString = "testing this string <b>that should</b> <lin>:match</lin> very with a string, but the <lin>:match</lin> isn't what so simple, it <b>needs</b> to replace a certain <lin>:match</lin> (can be the first, seconds... anyone) in the whole <b>text</b>"
Local $sSubst = "$1$2$3$4$1REPLACE$3"
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