Wow, you did some serious research!
It seems that most sites quote each other, or the Apple II (!) keys. (ctrl-X and ctrl-Y work only on the Apple II.)
Seems like they didn't even try the codes.
Meanwhile, I disassembled the game, and found out how to enable cheats. (And that which keys do something.)
First, make sure you're not in the intro.
Then, press both (left and right) Amiga keys and shift-Q (all at the same time) to enable cheats.
The status bar will show "MEGA DRIVE ENGAGED" if you did it right. (Is this a reference to SEGA Mega Drive? Or MEGAhit?)
First, the regular (non-cheat) keys:
esc: pause
space: show remaining time
ctrl-A: restart level
ctrl-Q: quit/reboot (also in intro)
ctrl-R: return to intro
ctrl-S: sound on/off
ctrl-V: show version
ctrl-G: save game (on levels 3..13)
shift-L: next level (until level 4, decreases remaining time to 15 minutes)
ctrl-L: load game (in intro)
"|" (shift-\): pause (also in intro)
Now, the cheat keys:
shift-W: slow fall
shift-I: toggle upside down
w: show good ending
d: show bad ending
,: decrease music index
.: increase music index
m: play selected music/sound
(available indexes are 0..56)
-: decrease remaining time with 1 minute
+ (shift-=): increase remaining time with 1 minute
1..9: skip 1..9 levels
F1..F10: displays "NO ACTION" (?)
r: revive (if dead) or get more HP (if alive) like a big potion
s: toggle hiding non-animated objects (buggy)
h: show DHEAP USED (amount of allocated memory?)
c: show numbers of current and adjacent rooms
shift-C: show numbers of diagonally adjacent rooms
k: kill guard
arrows: look at other room
(You might need to change the settings of the joystick for this last one.)
Finally, I searched the web for "MEGA DRIVE ENGAGED" and the only result was this:
http://www.elfqrin.com/docs/FreePlay.php -- FreePlay - Cheats, Tips and Tricks for classic games (in Italian)
It seems to have a different list of cheats than the other sites. It's incomplete, but at least it shows that the author tried them.
Extra: you can skip levels until you get to the demo level.
You can't control the kid, but you can use the cheats.
If you kill the guard with k, the kid will start to turn around endlessly.
