Answering my own question based on help from comments:
- Open and close the file without making any changes so that if file doesn't exist the file is created.
- Check the file size, 1 byte = 1 digit (stored in UTF-8).
- Read appropriate number of bytes, make changes as needed, etc. ]
- Error 2030 avoided! :D
Thanks to @Vesper and @Craig
*****Edit*****
Realised you don't need to close the file in the first step...
*****Edit2*****
Not UTF-8, ASCII