On the original V7, there are limits to that. The default characters are erase #, kill @, interrupt DEL (commonly represented as ^?).
You can change erase to ^H. You cannot change erase to DEL, which is what many modern terminal emulators send; tmux even outright forces DEL. This is partially because the interrupt character is DEL and that is hard-coded inside sys/h/tty.h. However, even after changing that, rebuilding the entire kernel with make all, changing src/cmd/{getty,login}.c to use DEL for erase, I still got erratic behavior. I'll have to comb through sys/dev/tty.c sometime and see if I can pinpoint the issue that blocks DEL for erase or if there's something in the build setup.
