Hast dir doch die Antwort selber gegeben:
[autoit]$Value1 = IniRead(@ScriptDir & "\test.ini","Dateiname","Wert","")
$Value2 = IniRead(@ScriptDir & "\test.ini","Dateipfad","Wert","")
IniWrite(@ScriptDir & "\test.ini","kompletterPfad","Wert",$Value2 & $Value1)
MfG