The cricket sounds are possible by changing the ambient noises of the game. But, despite the game being able to recognize what time is night and changing the ambient lighting accordingly, the sounds can't be coded to start at night without coding the sound's start and end routine of the transition process from daylight to night.
But as for the shadows...
Shadows would require a shadowmap. There'd have to be a shadowmap added to every object(If no object currently has a shadowmap)... But I don't know for sure, as I've never made shadowmaps.
The game will have to perform checks on every object to see what shadow it would create depending on the time of day(FeralHeart's "ambient lighting" code responds to changes in the time of day, more specifically sunrise, midday and sunset, showing that the game knows exactly what ingame time of day it is and changes ambient lighting accordingly). Shadows may be possible with access to the OpenGL rendering subsystem code of the game, and quite possibly the ability to update the version of OpenGL rendering subsystem the game runs with.
BUT: We'll have to consider the things that'll slow down the game. The time it takes to load maps would be increased as the shadowmaps are loaded, and the object positions determined for accurate placement of shadows, then the deciding of the position of the shadow according to the time of the ingame day, and that check of shadow position may cause midday and sunrises/sunsets to cause lag.
Shadows would be so demanding that FeralHeart may not run well with shadows. Gui's preset loads longer when the preset file is bigger, and the size of the preset file is dependent on the images inside, so larger images cause more loading and having more images can also increase loading times unless those extra images are just one pixel(In which case the load time increase is barely noticeable). If the shadowmaps are large files then that'll take a toll on load times, potentially cause crashes(I crashed when loading Gui's preset into a detailed map, but was fine when Gui wasn't wearing the preset), then the shadows could become as rarely activated as water reflections.
Would shadows catch anyone's eye? Does anyone look at water reflections when they walk past?
And that's all the problems I see with shadows.
