@~Sarf~ u must use XS++ v 3.1 and these files:
Downloads - R6BC002_RED52 - Top Sony Forums
Downloads - k790custpack - Top Sony Forums

First flash File System: K790_R6BC002_FS_AMERICA_2_RED52
Customize File System: HB1-06_Generic_CDA102568_107_R4A_GENERIC_AMERICA_2
Finaly flash Main: K790_R6BC002_MAIN_GENERIC_EV_RED52

Remove SIM-lock patch generator - Top Sony Forums

1. Select phone model - K790.
2. Click Identify
3. Mark Bypass DB2020 security
4. Add Main ( K790_R6BC002_MAIN_GENERIC_EV_RED52.mbn )
5. On MISC files add Quick Access patch.vkp
6. Click Flash hold "C" and plug USB cable.

After 3 - 4 min. Setool say to unplug cable, reinsert battery and click READY then again hold "C" and plug USB cable.

Then click NO to apply patch and wait ~ 20 min.

After all you have Quick Access patch and can apply patches (*.vkp)

1. Select phone model - K790.
2. Click Identify
3. Mark Use "quick access" patch
4. On MISC files add Remove_SIM_lock_K790_R6BC002.vkp
5. Click Write SCRIPT

NO - to apply patch