This is a very good point. If you're porting the same game, something must be changed. there would have to be some kind of strict rule set on that. Maybe have it so the game can only be an emulation form where the original code is used
I think what you would have to do is separate the underlying architecture from the functional game. so you could change as much of the code as you want it as long as the presentation itself is less than some percentage altered not to include updates like display resolution.
So you could update netcode, adapt it to a new os, improve matchmaking, whatever... as long as the look and feel of the user facing presentation remains the same. Or you could upscale the graphics to work on a newer display, as long as you don't physically alter the original models or sprites.
the less than some percentage change would be in there to allow you to do things like update settings icons to match the buttons of the console you're porting to without that technically counting as a change.
That sounds like a pain in the ass to do lol. I could see there being many court cases and where people are arguing percentages to a judge lmao. But hey, it would give us TMNT on virtual console. ---