OpenFile() returns a file handle that allows both reading and writing, and then you use seekfile to go to a specific location within the file.
However I don't know if it is possible (don't think that it is) to 'insert' data into a file so that offset of the rest of the data in the file shifts as well.
However I don't know if it is possible (don't think that it is) to 'insert' data into a file so that offset of the rest of the data in the file shifts as well.