Is it possible to access the real ending of Alien Syndrome on Game Gear without "cheats"?
Solution 1:
Everything that I have found on writeups, walkthroughs, etc suggest that the configuration menu where you can change the mode can only be accessed by knowing the code.
Gamespot
Cheat Database
Console DB
And so on.
So apparently on the port (Which is more of a sequel than a port), it's only accessible by a code/cheat. I wasn't able to find any writeup that says otherwise.