Instead of an APPEND file command, it might be nice to have the OPENFILE command to include read and write as an option, instead of just read or write. A bit like the C file system commands. That would allow people to do their own 'appending' by allowing them to read up to a point, then writing over parts as you can in C.
I realise we've already talked about this in that other thread, but thought I might as well make it an official suggestion. :)