[Xperia Pro MK16i] Several questions about firmware, OTA update and customization - Sony Ericsson Xperia Neo, Pro

Hi everybody
I own an Xperia Pro MK16i. The phone is still on stock ROM (4.0.2.A.0.58 GB 2.3.4) and the bootloader is still locked. The only thing I did recently is root the phone successfully with eRoot.
Now, the phone still gets the OTA updates, right now it does notify me that the "new" update 4.0.2.A.0.62 (the latest GB release available for my phone) is ready to download. I would like to install this update in order to try it and only after eventually switch for ICS 4.0.4 (4.1.B.0.587 is the latest).
I was wondering myself:
1) Is there any way to backup the OTA update in order to save and store it for the future? I red that OTA update files end up in the /cache folder and thank to root access I managed to open that folder and see that as soon as I download the OTA update a download_package.bin is created inside the folder; the problem is that the file is less than 8MB and it's a BIN file. What this file is for and is there any way to make use of it? The only thing I know is that it's too small to be the real firmware/rom...right?
2) Is there any chance for me to get somewhere the 4.0.2.A.0.62 stock rom with the proper customization number? My phone is unbranded and purchased in Italy where I live, customization version is: 1249-7782_R12D
3) What does this customization mean? Is it about language? About preinstalled apps? Or what? Someone could clear me the whole thing please?
Many thanks

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goriath said:
1) Is there any way to backup the OTA update in order to save and store it for the future? I red that OTA update files end up in the /cache folder and thank to root access I managed to open that folder and see that as soon as I download the OTA update a download_package.bin is created inside the folder; the problem is that the file is less than 8MB and it's a BIN file. What this file is for and is there any way to make use of it? The only thing I know is that it's too small to be the real firmware/rom...right?
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OK, I digged around about this point and just for reference I share what I found.
The main problem with OTA updates is these packages are binary DELTA packages; they are not the full ROM/FW release, but they contain only the differences between the source ROM (the firmware installed in the phone) and the target ROM (the updated firmware you want to install in the phone).
I took a look inside the BIN file with an HEX editor and what I found confirm the dependance between the update and the stock ROM:
<?xml version="1.0" encoding="ISO-8859-1"?>
<metadata version="3.2">
<product>
<manufacturer>SonyEricsson</manufacturer>
<model>MK16i</model>
<hwplatform>MSM7x30/8x55</hwplatform>
</product>
<update>
<generation>
<version>2.0.0.24</version>
<date>2012-02-01T11:01:38+01:00</date>
<rb_version>6.2.29.19</rb_version>
<rb_ua_version>6.2.29.19</rb_ua_version>
</generation>
<source>
<software>
<revision>4.0.2.A.0.58</revision>
</software>
<customization>
<variant>1249-7782</variant>
<revision>R12D</revision>
</customization>
</source>
<target>
<software>
<revision>4.0.2.A.0.62</revision>
</software>
<customization>
<variant>1249-7782</variant>
<revision>R12D</revision>
</customization>
</target>
</update>
</metadata>
This explains why my download_package.bin is large only 7.55MB; it does update (add/replace files to) the actual ROM. And this is the reason why updates through OTA are sequentials; I cannot install latest GB OTA update w/o go through every previous update first.
So this binary package alone is not useful to create a full ROM of any sort, cannot be flashed as is and cannot be extracted/unpacked/decrypted unless to be a developer and doing reverse engineering.