If you just don't want other people modifing your code, I can understand that and as was mentioned, you can use custom loader and some obfuscation techniques but there is a limit to what they can do. One thing I should mention is there is a version of SQLite that supports encryption, so you can protect your database that way. You can find one such version (one I used and works great) here: https://github. com/utelle/wxsqlite3/tree/master/sqlite3secure
But if you are really just worried about bug reports and nothing else, then I recommend you include checksums as mentioned above + release two versions of the game. Aurora C# that would be the original version released by you and Some other name, that would be version meant for modding. You could even make it opensource if you want or not if you don't. Because it would have different name and presented as different game, it should be much easier to distinguish which bug reports you should handle and which should be redirected to the community.
Of course, this is purely a suggestion related to the bugs. I don't think you owe us anything, not even an explanation and should allow or disallow modifications as you see fit and feel like.