MTW on windows 8.1

[Stazi]

My question: can they cure my current game or would they harm it? And if they do harm it, does it mean I will have to buy the game again?

Those files can't harm the game or your saves. Make backup of the old ones and try them. They probably won't make a difference but.. who knows. I've bought my copy of Steam MTW like two weeks ago and I've been testing it till now (mainly with Redux mod). Steam release has a new, rewritten graphic engine which gives you significantly better performance. Especially, late game campaign map with huge amount of units' stacks, agents, castles etc. works a lot faster, smoother. Of course the new engine brings their own bugs. The patch CA released 3 months ago helped some people and broke the game for the others so CA gave us a roll back option. If the latest version crashes for you, try restore a previous version. Here is the thread on the official TW forum.
Just remember two things: 1. right-clicking can be deadly , 2. Radeon/AMD is still superior to all other video chips manufacturers when trying to play MTW.