Just relock the bootloader and you can update the phone with Sony Update Service.
However my problem after unlocking the BL again the phone still offers the update to be installed even it is already there. Any idea how to fix this?
Using Samsung Galaxy SIII (Slimkat 4.4.4 Build 7.8, Yank kernel 1.7a-beta3) and Acer Iconiatab A700 (CM 11 Nightly)
2nd device: Samsung Galaxy S (Slimkat 4.4.4 Build 7.2.1, Semaphore Kernel 3.4.3s)
Business phone: Sony Xperia SP (Official Firmware 12.1.A.1.205, DooMKernel v13)
Retired Devices: Sharp Netwalker, Sharp Zaurus C1000, Openmoko Freerunner, Motorola A780