4 months ago, critor released mySpire(http://www.cncalc.org/forum.php?mod=viewthread&tid=9441) which allowed modification of nspire CX/CM’s boot splash screen. Since the image itself is signed, there is no way to change the image except modify its position, size, etc.
However there is still a workaround. It’s possible to use third-party payload to display extra things on the screen. So here it is.