[Upgrading, Modifying and Unlocking] Doggy77:
The Update worked today, but I had to edit the ZIP-File. The version of CWM that was provided by harddisk_wp (http://xdaforums.com/android/help/root-cat-b15q-root-proper-t2989763) seems to have an error (see below for more information). The "root" was preserved and available after reboot. The apps that were moved to SD-Card 2nd Partition using link2sd had to be reinstalled, which was possible without dataloss (in my case e.g. "Threema", it had conserved all conversations, keys etc.). CWM was replaced by stock recovery.

The way to update was not very easy but I learnt a lot of things. Here my experience:

I had my B15Q equipped with CWM without swapped partitions, ROM 022 and root (SuperSU).

Every OTA-Update to 026 or 032 failed due to "signature error".

I transferred the ZIP to the SD-Card (Attached the B15Q as MTP-Device to Windows and copied the "update-022-032.zip" ZIP to the "SD-Card"). After booting to CWM I tried to flash this ZIP which failed, because of

script aborted: This package is for "CatB15Q" devices; this is a "MTK".
This package is for "CatB15Q" devices; this is a "MTK".
E:Error in /sdcard/backups/update-022-032.zip
(Status 7)

The file "/system/build.prop" contained the correct value for "ro.product.device", but the CWM has an error within the method getprop("ro.product.device"), it always returns "MTK" instead of reading the correct value from "build.prop". The update...zip contains a script file where this property is checked and should be "B15Q". Because the values mismatched ("MTK"!="B15Q") the script refused to update and aborted.

I had to edit the file "/META-INF/com/google/android/updater.script" inside the ZIP and remove this line:

getprop("ro.product.device") == "CatB15Q" || abort("This package is for "CatB15Q" devices; this is a "" + getprop("ro.product.device") + "".");

I Used 7-Zip, did NOT unpack the zip but "Open" it in 7-Zip, navigated to the file and chose "open External" in my favourite editor "Notepad++" (to make sure to preserve the line breaks).

After this change was done I transferred the ZIP to the SD-Card (Attached the B15Q as MTP-Device to Windows and copied the modified ZIP to the "SD-Card"). After this I rebooted to recovery (CWM) and selected the modified ZIP to be flashed. It needed about 10 Minutes to flash it and after it was finished finally I was able to choose "reboot now" within CWM.

I stood there, fingers crossed and after some waiting time the devices finally showed "Android is updating... Optimizing App 1 of 164". About 10 Minutes later it was responsive and worked. Checked su using "Terminal Emulator" and "Ghost Commander" to edit a file within "/data/data" which was possible without error.

The "About my phone" now shows "Build Number CatB15Q_GENE_DS_1.032.000".

The native "App2SD" is now working also and I am happy about my new version. The recovery boot loader (defective CWM) was replaced by stock loader, so I hope the OTA update will work now.

tl;dr:

Update worked, had to edit the ZIP because my CWM had an error determining the correct product ID.

Root was preserved and still working, CWM recovery was replaced by stock recovery.

Best regards,

Markus "Doggy77" Seifert