Depends on what makes the game "terrible" to begin with. Was it a great table with bad code? If so, then yes. If it had a terrible layout, terrible shots, horrible sound, and one time slapped your mother, than a code update may not save the game.
However, my next purchase in a few days was decided upon strictly because I keep reading on how the code change made this dud a winner.
From - https://pinside.com/pinball/forum/topic/high-roller-casino
"Played this with the v2 ROMs and the V3 director's cut version and it's a night and day difference - like a new machine. Definitely a fun machine and worthwhile - but you have to have the V3 ROMs for this machine. It was definitely a labor of love for keefer. "
That, and about a baker's dozen other similar threads sharing the same sentiment made me put a deposit on the machine AND contact my local guy for the V3.0 ROMs to be whipped up today so they're here a day after I get the machine.
So long answer to your original question... yes, code apparently can save a terrible game. Hope TWD gets/got some similar love.