what are your thoughts on this mod, per the OPs needs:
Local $sSplit = _StringEqualSplit_au3("12345678910", 3)
msgbox(0, '' ,$sSplit)
Func _StringEqualSplit_au3($sString, $iNumChars, $var = "sSplit" & $iNumChars & "Var")
If Not IsString($sString) Or $sString = "" Then Return SetError(1, 0, 0)
If Not IsInt($iNumChars) Or $iNumChars < 1 Then Return SetError(2, 0, 0)
Return "$" & $var & " = " & stringtrimright(StringRegExpReplace($sString, "((?s).{1," & $iNumChars & "})", '"' & "$1" & '"' & " & _" & @CR) , 4)
EndFunc
And this version with &=
Local $sSplit = _StringEqualSplit_au3("12345678910", 3)
msgbox(0, '' ,$sSplit)
Func _StringEqualSplit_au3($sString, $iNumChars, $var = "sSplit" & $iNumChars & "Var")
If Not IsString($sString) Or $sString = "" Then Return SetError(1, 0, 0)
If Not IsInt($iNumChars) Or $iNumChars < 1 Then Return SetError(2, 0, 0)
Return "$" & $var & " = " & '""' & @CR & StringRegExpReplace($sString, "((?s).{1," & $iNumChars & "})", "$" & $var & " &= " & '"' & "$1" & '"' & @CR)
EndFunc