From the other topic, you could symlink the so.63, that might work.
If that doesn’t work, you can install the libicu-63.1 next to the libicu-66.1, though it might sound dangerous 
rpm -e libicu --justdb --nodeps
This will remove the package libicu-66.1 from the package-database but will still preserve the files. So all the software that depends on this will still work.
rpm -Uvh https://releases.jolla.com/releases/3.0.3.10/jolla/armv7hl//core/armv7hl/libicu-63.1+git5-1.1.6.jolla.armv7hl.rpm
This will install the older packae, which makes software that still depends on it run again.
After reboot it should get further in the boot process, but because it is partly new system and partly old, it might still not work great. But hopefully enough to get you going again.