how to play any game through Spacewars?

I saw in cracked online steam games (that use Steam's servers ig) we play through Spacewar. I then discovered that you can download a game through family share from a friend and apply a fix to the game. And then you both can play the game at the same time cause your both playing through Spacewars and not the game itself (both of you need the fix of course).

I tried doing some research and asking chatgpt and found the you can accomplish this by changing the hex code of the .exe file (changing the app id of the game?). Im not really sure about that to be honest. I also saw in a fix for left 4 dead there was a creamapi that had a "ID override" section. But I couldn't find any documentation on that

So basically, My end goal is to be able to play any game on steam while steam thinking im playing space war. Any help would be appreciated.