Unlike Android bootloaders and kernels, which is open source, therefre hackable, WP8, like Apple is a closed platform and kernel, therefore, unhackable to a certain extent. Usually locked to either the carriers own firmware changes or Nokias/MS own system locks.
The China version you have is the one which most UK carriers use (Electronic goods cheaper to put together in China/Taiwan), locked or unlocked, if you have one from Hungary its most likley an import hence unlocked, so itll probably have different characteristics such a removable battery or SD Card slot.. as they are built to that countries specifications where patent laws are not so strict.
Sim Free and Unlocked are NOT the same.. Sim Free means you can use any sim card in it, but the APN is still locked to the carrier (Using the carriers own Branded bootloader or kernel) which means your update will still most likely come from the carrier, hence why it may still run the same way because the carriers own Lock is still there.. sometimes if you look in Wifi settings, a branded device may have a set unchangable proxy address to tye carriers servers, so the device belongs to the carrier, not Nokia. Also check in Settings > About.. look at carrier: its still set to your last carrier (ORGGB - Orange and so on..) )even thoughi its SIM free.
Unlocked / Unbranded (Hungary device) means they are Open devices (Open Proxy or Open to Nokia servers) to Nokias servers and not bound to a carrier, so they can be updated by Nokia/MS without the update having to be checked and Software added in order to correspond to the carriers Hardware, such as different brightness settings or battery behaviour. Check About.. itll say something like GB or OPEN... Also check Settings > Extras and Info at the Correspodence ID, which is the same.
I am aware sim free devices can be unbranded but they must be rooted first and unlike Samsung or Android where theyre rooted then flashed with CWM or ODIN, its extreemely complicated using Windows Command Lines and 3rd party hack software and Unlike Android where they can be flashed back with a Stock rom, MS/Nokia will not repair them if you damage them
With regard to your "Nokia Glance", check the dimmer times and settings.. have you mised something.. if not, it may be a change in GDR3 from your carrier, as GDR3 is from MS, changed by your Carrier, Black is firmware from Nokia.
However, please check here:
Windows Phone 8 Development and Hacking - xda-developers
If you wish to try, but its a messy business and I dont want to be responsible for breaking your phone.
OR if you live in UK, try here to trade it in for an unlocked one:
https://uk.webuy.com/
The only WP8 device capable of being JailBroken / Hacked fairly easily is the Samsung Ativ S which can be Interope unlocked, but again thats another story
Whatever you decide to do though, good luck,
If you wish to discuss hacking/breaking bootloaders and kernels, Can I also recommend that you open a new thread as this may lead to a new discussion and is off topic of the OPs question
Cheers