The one I know of that glitched lines at the right time (the xbox 360 reset glitch hack modchips) worked by glitching the reset line at the right time via a CPL

The one I know of that glitched lines at the right time (the xbox 360 reset glitch hack modchips) worked by glitching the reset line at the right time via a CPLD that had been attached in such a way as to bypass the analog filtering. I agree that this scheme doesn't protect against hardware implants modifying lines, but the threat model discussed thus far was around propagation of software implants throughout a system.