Can they use same VRAMS???
But, one could probably mess around and get Prey Classic + Prey 2017 installed together, in a very slick manner.
Depends on what you have for resources available.
What's good is they both look like they use different PROFILE game-folders.
Prey Classic uses My Documents\My Games\Prey.
Prey 2017 looks like it uses My Documents\My Games\Arkane Studios\Prey, according to PC Gaming Wiki.
If you have Prey Classic from retail on disc - you could just install it off the disc anywhere and name the folder "Prey Classic" or something; grab patch 1.4 from 3DRealms (which makes the game DRM-FREE); and run the game. Then you could jump on Steam and add that version as a Non-Steam Game and you're done. Tried that; works fine!
Prey Classic Steam-version owners, it uses a different Prey.EXE which ain't DRM-FREE; doesn't work w/out Steam. Tried it, no dice. You'd need version 1.4 DRM-FREE version of Prey.EXE, to boot the game without Steam going.
If you have both Prey Classic for Steam-version + Prey Classic at Retail w/ Patch 1.4, you could chuck the DRM-FREE file for Prey.EXE from your retail-version right into the Steam-folder and be golden - tried it, it works. Then, of course - rename game-folder to "Prey Classic" + add it as Non-Steam game (so this doesn't conflict with Prey 2017's folder).