Offtopic, but does anyone know of a way to ensure I don't introduce non-ASCII filenames, to ensure broad portability across systems? I've had to resort to disabling UTF-8 on Linux to achieve that.
You can't really "disable utf-8" on Linux. You can change how things are encoded when displaying or saving. (via locale/lang variables) But if the app wants to create a file named "0xE2 0x98 0x83" (binary version of course), it's still free to do that.
You could probably write some filter using fusefs, but in practice... I think you should configure the servers / clients to agree on encoding instead. Better supported and shouldn't be that much work.
But it won't allow you to force ISO-8859-1 in this form. However you could filter out non-ASCII characters.