You should be able to hit F8 while booting the machine and this will let you say yes or no to each of the commands in the autoexec.bat and config.sys files as they load.
By saying "NO" to anything that looks like a BMDC control command, you can bypass the loading of the machine control sofware and go directly to DOS.
Anybody with DOS experience should then be able to use EDIT or some other text editor to fix things.
In our case, we loaded a copy of DOSSHELL into the DOS directory on the HDD. We use like it as it is a GUI that is free and lets you do a lot of maintenance real easly.
Doing the F8 at boot enables you to bypass the loading of the BMDC stuff which may be of some benefit for some operations - DEFRAG and SCANDISK are such diagnostic and repair programs that are better to run out of DOS prompt than while the BMDC program is running.