Default Why does changing build.prop fingerprint invalidate the rom/booting?

if i change the build fingerprint in build.prop it leads to an unbootable rom. Just black screen after kernel. ADB boot log doesn't show anything useful (but its running). I've wiped all caches before booting.

What's happening here? Why is the system corrupt once the string is changed?
Galaxy S4 LTE+ I9506:
Snapdragon800 || MSM8974
2.3GHz || 2GB Ram || Adreno330
Cyanogenmod 11