AFAIK we have no bug confirmed for file_appendfront, so it should work as described. It's normally used to add records in front, and zero length will most likely add nothing.

I am not sure what you mean with the EOL issue. Your string has no EOL. For this, let it end with \r\n, or 0x0a 0x0d. The function just adds what you pass as argument. It does not care about EOL or other character sequences.