Very few people even bother to use the 534C because it really doesn't do anything or give the game anything more than the 534B. Meaning that whatever is in the 534C is just modding the 534B a bit. No advantage. As Age said, it's not an official patch.
I've never played around with the 534C, but from what I hear, any ships pre-speced for 534B can be used without any tweaking in 534C.
The worse thing that happens is that the ship shows up in the invalid shiplist text file in the game's root folder.