Hello EndlessTime,
I believe you may also have posted a comment to the trailer? In that case, YouTube decided that I cannot reply to it for some reason...
You are very welcome to change anything you'd like, as long as you follow the lincense it is under. This, however, will only be of concern if you are sharing anything. I recommend downloading the source code through my GitHub- that way you can change whatever you want. The locations of all assets should be fairly straight-forward, i.e. textures are in the textures folder.
If you downloaded the game through itch.io, you can also change textures and sounds, though not text.
Looking forward to see, what you'll do with it.