This is very cool! :^) One way to set the file ID number inside KB9, before a SAVE, is to POKE 10052,xxx in immediate mode, where xxx is any decimal number 1-255. This will overwrite the file ID preset of $FE in KB9...at least on my copy of BASIC, which I got from Jim McC. To LOAD that specific ID, POKE 10135,xxx. I just tested on a file saved to cassette with ID $7F (POKEed 127 dec.), verified with Butterfield's DIRECTORY program, then reloaded and it skipped over two other programs and LOADed the proper one.
I guess that this only works if your patched version calls the 1541 routine after KB9 sets up its file ID and jumps out. On my copy of BASIC, that's $27A3 and $275C for LOAD and SAVE, respectively.
See ya, Dave