Q:

How to install Steam games on external HDD without having to rerecognise files?

I have a decently capable laptop which I upgraded to an SSD a while ago. Unfortunately, I didn't have the foresight to buy a 500GB 850 EVO and I now have a 250GB. I now want to install games to use on my laptop, and I know that I can do this with a Steam library on an external HDD.
However, when I tried this, Steam would complain whenever I tried to unplug the HDD, forcing me to re-recognize the game files when I plugged the HDD back in. That takes a while, especially on a 5400rpm HDD over USB 3.
Is there any way I can avoid having to re-recognize game files while still only having the external HDD plugged in whenever I want to play games? I would love to be able to keep Steam open, as the notifications and friends panels are useful to me while I am not playing games.

A:

According to an answer on the LTT forums, it is relatively easy to accomplish by creating symbolic links to the external HDD game folder files. (slightly paraphrased and adapted from original)

Close Steam and plug in an external drive (with games already installed to it)
Find the game's appmanifest file in the [External SteamLibrary path]/steamapps folder. The number in the filename is the same as in the Steam Store page URL

e.g. BioShock Remaster's URL is store.steampowered.com/app/409710/BioShock_Remastered/, and the number is 409710

Move the appmanifest file to the local storage.

e.g. from [External SteamLibrary path]/steamapps/[appmanifest file] to C:\Program Files (x86)\Steam\steamapps\[appmanifest file]

Open a Command Prompt as administrator
Change directory to the local Steam library's common folder

e.g. Type: cd "C:\Program Files (x86)\Steam\steamapps\common" 

Create a symbolic link using the command mklink /J  [game folder name] [Path to game on external HDD].

e.g. Type: mklink /J "Bioshock Remastered" "[External SteamLibrary path]\steamapps\common\Bioshock Remastered"

Repeat steps 2-6 for more games

