as the title implies - i’ve had the mod version for a while, bought the retail version and haven’t actually installed it yet since i didn’t want to re-download the whole thing.
i’ve gone through a similar procedure before with other games that weren’t sourcemods, but trying with BMS today i haven’t been able to get steam to recognize the files i already have. (mind you, what i did so far is put the BMS folder in steamapps/common, renamed it to Black Mesa, tricked steam into generating an appmanifest with the game’s id, restarted steam, then attempted the installation)
i do realize there are some files that i’m going to have to download either way, but i’m currently on 300 gigs per month on a network with 3 other people (not my choice of internet plan) and so the full 13 gigs is something i’d like to avoid downloading unless i really have to. i feel like this was probably a common inquiry when the retail version first came out, but i haven’t been able to find any information here, on the wiki or on the steam community