I found a loophole to run the game without replacing "GameAssembly.dll":
You need to create an empty file "System.smg" on the path: "C:\Users\<%USERNAME%>\AppData\LocalLow\KsT Games\Seaside Mystery\"
I tried it, but unfortunately the game says I haven't linked the account. I've renamed the folder once with spaces, "Seaside Mystery," and again without spaces, "SeasideMystery," but neither works.