You could try to change the default-charset within the user-properties in tab export but beside utf8 there is only unicode and ansi available and I doubt that this will be useful in your case.
If you really need windows-1255 as charset you will need to convert the qlik-export with any third-party tool (some editors like notepad++ and their plugins are quite powerful to convert data and it may be also posible to automate such tasks).
But I think this approach will be quite expensive so I would look if there could be changed anything else in your process to use the native qlik-output.
You could try to specify your codepage within the second parameter of the export-statement whereby I'm not sure if Qlik will use any other than 0, 1200 or 65001 and which requirements it might need. I think the codepage must be available on your machine and also region-settings within the OS might have an impact.