This topic comes up regularly, and it would be great to see a working method implemented.
As of version 3.02, neither of those things.
The N64 has to be modded in order to have a button combo reset.
Not necessarily. Since the Everdrive 64 emulates a Gameshark, then you could use a Gameshark code to test for the given button combination of joypad buttons, and then reset if those buttons are all pressed at once. But since the Gameshark codes are stored in the N64's RAM then you'd need numerous different codes, or rather the same button test codes but stored at different places in the N64's RAM, to prevent any given game overwriting the area of memory where the button test and reset codes are stored.
I've never written any gameshark codes, so I don't know how difficult it would be to find a safe area in any game's code, but logically I'd have thought that any N64 game that doesn't use the expansion pak's 4MB of RAM (such as Super Mario 64, Mario Kart 64, Doom 64, Goldeneye, etc) would be OK if the Gameshark's codes were placed in that extra 4MB of RAM, since those games never touch that RAM anyway. It might even be that just one single Gameshark code (i.e. check if all of the buttons in the required combo were pressed at once, and if so then reset the N64) would work for every game that didn't make use of the expansion pak.
Is there anyone on these forums who is knowledgeable about such matters?
There are other ways to remotely reset an N64, have a look at:
http://krikzz.com/forum/index.php?topic=9631.0