#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?m)(?<prefix>{[^\\}]++)(?<first_lvl_command>\\\w+(?:\[[^]]++]?({(?:[^{}]+|(?3))*+}))({(?:[^{}]+|(?3))*+})?)(?<closing_bracket>})"
Local $sString = "\rpl{text}{ some\com1[opts]{ some \qtyrange{100}{200}{\celsius} and }{something else \gls{abc} $1=1$ not \colortext{\red}{\underline{text}}}} but this is already braced {\qtyrange{100}{200}{\celsius}}}" & @CRLF & _
"" & @CRLF & _
""
Local $sSubst = "$prefix {$first_lvl_command$closing_bracket}"
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