As far I understand right:
You’ll only flash only blobs *). After that you’ll just update the SFOS 4.6.0.15 to SFOS 5 as OTA. But things can be more complicated of course outside my understanding. Or vise versa.
*) fastboot flash oem_a SW_binaries_for_Xperia_Android_14_5.4_v?a_zambezi.img