XPERIA 1 III FLASH REGIONAL FIRMWARE WITHOUT UNLOCKING BOOTLOADER

This guide originally from @Forbesii of xda forum
Things needed:​
1. An Xperia 1 iii
2. A Windows PC (I don't know if there's a Mac or Linux version, but I didn't find it)
3. ADB Driver adb.clockworkm...
4. A reliable USB-C cable
5. NewFlasher
Download: [TOOL] Newflasher forum.xda-deve...
Latest: V55 download it.
6. XperiFirm
Download: Tool Archives - XperiFirm Tool
xperifirmtool....
Latest: V5.6.5
UPDATE FIRMWARE WITH THE SAME REGIONAL VERSION WITHOUT LOOSING YOUR DATA
open cmd and go to the path of the firmware then type and run: newflasher set_active:a otherwise your phone will boot into a bootloop.
TO KEEP YOUR DATA WHEN UPDATING FIRMWARE(FOR THOSE ON THE SAME FIRMWARE0
If you only delete userdata.sin, your data partition will be corrupt and you will be forced to factory reset and lose all your data.
To prevent this from happening, not only do you have to delete userdata.sin, but also appslog.sin, diag.sin and metadata.sin from the firmware folder as well.
Found this by checking the update.xml file in the firmware folder, all required sin files to delete are listed as "NOERASE".
Power off your phone and plug it into your PC. Hold the volume down button and the power button until the LED turns GREEN.
Now you can double click on the newflasher.exe in your ROM folder and follow the guide. You can keep user data while flashing, just pay attention on the instructions on the Newflasher.