So the method you've shown us only works on dashingdon right? What about the game I downloaded from CoG apps?No problem at all!
I'm not entirely sure as to what you're asking but I'll try to answer to the best of my ability. Feel free to ask again if you think I misunderstood your question.
I suppose it would work on full games if there is a dashingdon link, but I can't say I've really tried. Aside from a handful of exceptions, you won't find many finished games on dashingdon. I normally buy the full games on steam if I like the demos since I can sync it up + download it on my phone too. There is a save editor that I like to use sometimes. You can do that or simply get a mod.
The methods I mentioned for twine games should still work with a full game if there is a save to disk function.
Also, does the game downloaded from Steam can be modified?