Global $Str="aaaabbbb"
MsgBox(0,'',__StringInsert($Str,"c",4))
Func __StringInsert($String,$ins,$Position)
Local $aString=StringSplit($String,""),$ReturnStr
For $i=1 To $aString[0]
If $i=$Position Then
$aString[$i]&=$ins
EndIf
Next
For $i=1 To $aString[0]
$ReturnStr&=$aString[$i]
Next
Return $ReturnStr
EndFunc