I can now state from personal experience, that debranding your Firmware invalidates your Nokia warranty, and even if the original Product Code is set using NSS after de-branding, the Nokia engineers can detect what has been done, and return your handset UNREPAIRED and with a voided warranty.
I had debranded from Orange UK to EURO1 variant last year, and was up to V21 FW when my handset developed a screen fault.
I reset the product code to my original (Orange UK) code, but could not downgrade the FW back to an Orange UK Variant.
I sent in the handset the the main UK NCC (Thorbury Freepost service). Apart from the screen fault everything else worked perfectly.
The handset was returned yesterday with a note saying
"Please note your phone has not been repaired. After inspection by an accredited engineer, it is deemed to be outside the warranty conditions.
Mobile phone IMEI xxxxxxxxxxxxxxx Product Code xxxxxxx has been refused repair due to the following:-
Unit has been received with incorrect software.
Unit has higher software than authorised."
Not only is my warranty void, but now the handset is bricked and will not boot. (Presumably the NCC attempted to re-flash & downgrade the FW)
Be warned folks, debranding is great unless you ever need a warranty repair... 😮