Good system administrators always have a viable fallback plan to cope with failures. A mistake configuring the serial console can make both the serial console and the attached monitor and keyboard unusable. A fallback plan is needed to retrieve console access.
Many Linux distributions allow boot diskettes to be created. Writing a boot diskette before altering the console configuration results in a boot diskette that passes good parameters to the kernel rather than parameters that may contain an error.
Under Red Hat Linux a boot diskette is created by determining the running kernel version
and then using that version to create the boot diskette
Under Debian GNU/Linux the boot diskette is created by determining the version of the running kernel and then using that version to write the boot diskette
An alternative fallback position is have a rescue diskette with the machine. A common choice is Tom's root boot.