As the title says can we use template project from other users, for example on the godot asset library there is a 2D platformer toolkit . Are we allowed to use this as our base and changing it our should we code everything from scratch. Or are some assets alright, but something this big isnt.

Thanks

You can use any assets you like (as long as you have the legal right to use them). This includes code assets and game samples. Obviously, and as you already mentioned, game samples need to be changed so we don't end up with multiple submissions for the exact same game (it happens) :D