ui_print("Verifying current system...");
getprop("ro.build.fingerprint") == "YotaPhone/yotaphone2/yotaphone2:5.0/LRX21M/5.0.0-EU1.1.39:user/release-keys" ||
getprop("ro.build.fingerprint") == "YotaPhone/yotaphone2/yotaphone2:5.0/LRX21M/5.0.0-EU1.1.44:user/release-keys" ||
abort("Package expects build fingerprint of YotaPhone/yotaphone2/yotaphone2:5.0/LRX21M/5.0.0-EU1.1.39:user/release-keys or YotaPhone/yotaphone2/yotaphone2:5.0/LRX21M/5.0.0-EU1.1.44:user/release-keys; this device has " + getprop("ro.build.fingerprint") + ".");
So basically if those lines were to... disappear... then the update process should just skip that check...
Is it possible? Can the update be modified and repackaged?
Edit: Now that I further investigated the file, for me the update fails on the fingerprint check if it's tried to flash via adb sideload. If the OTA process is allowed to do it's job normally, the update process halts to this line:
(range_sha1("/dev/block/platform/msm_sdcc.1/by-name/system", "2,0,1") == "20cf74300e388ef1140796901a2c8a2e8a423ead") || abort("/dev/block/platform/msm_sdcc.1/by-name/system has been remounted R/W; reflash device to reenable OTA updates");
So... Any idea what it means? What's going wrong?
Edit2: Ok. I can confirm that the updater-script can be modified and then be executed. Basically all the checks on system-partition have to be removed. I did not, however, dare to go through with this. Mostly because I am not fully comfortable making these changes and rather not try these out on a 700 euro phone. If it successfully updates some of the images, but fails on the others, it might just brick the device.
If someone wants to try out, download the OTA update on your phone, grab the .zip from /cache/update/, modify the updater-script in folder \META-INF\com\google\android\ inside the .zip, sign the package again with testkeys following SteadyQuad's instructions, and finally try to flash the zip via adb sideload from the customized recovery from the opening post of this thread. Easy, right?
I think the safest method to do this would be to restore the system partition to it's original (Read-only) state and then try the OTA update normally. Any idea where one could find the original system.img for lollipop?
Edit3: My monologue continues: to answer my own question, the Lollipop firmware can be found here.