MS-DOS did have a function to change the option character (INT 21h, AH=37h) [1], and the "kernel" always accepted both '\' and '/' as a path separator (and that is still the case today; the shell however, is another story). The same call can also change MS-DOS to require "/DEV/" before device names. [2]
[1] Documented for MS-DOS 2.0; documentation removed for MS-DOS 3.0; still available (according to my source) through at least MS-DOS 3.30
[2] God, why do I still remember this information thirty years later? Sigh.
[1] Documented for MS-DOS 2.0; documentation removed for MS-DOS 3.0; still available (according to my source) through at least MS-DOS 3.30
[2] God, why do I still remember this information thirty years later? Sigh.