In my code I have:

cassette: equ 0

if cassette != 0
        db 0x1f, 0xa6, 0xde, 0xba, 0xcc, 0x13, 0x7d, 0x74
        ds 10,0xd0
        db 'mld   '
        db 0x1f, 0xa6, 0xde, 0xba, 0xcc, 0x13, 0x7d, 0x74
else
        db 0xfe
endif

With the sole purpose of either generating a .cas file or .bin file. It would be great if the definition of cassette could be specified on the command line.

I would imagine an option -Dcassette=1 which would set cassette as requested, much like the c preprocessor.