I think I just made a massive error. I bought SiN episodes on Steam because it was the only way to get the original SiN (I still have the original disc but figured it probably wouldn't have worked). Now I've just discovered not only does the Steam version not come with the expansion but it has also been censored with lots of textures being replaced for nudity and license reasons.

Can I somehow edit those textures back into the Steam version from the content on my disc?

Is the GOG version uncensored?

The GOG version is uncensored. Now is the perfect time to pick it up, either for 5 USD on sale or perhaps even less if you catch it on the rolling flash saves going on at present (Summer sale).