[OnePlus 12] alejandrobass:
Hey there everyone, it's my first thread on XDA. With CN set buyers getting more and more common, I hope many find this thread useful. As a CN set owner myself, I would like to share some of my personal experience with flashing rom and dealing with bootloader.

First off, I would like to share some of the tried-and-true methods of flashing from stock ColorOS rom to OxygenOS rom. First of all, thank you @Canuck Knarf for the thorough guide on unlocking bootloader. Then, I would like to thank @snowwolf725 for the rom conversion script modified from @Canuck Knarf and also the download like provided here.

Secondly, these partitions are NOT to be tampered with no matter what. They are:

persist

ocdt

modemst1

modemst1

The conversion script provided by @snowwolf725 does not touch any of those, I can confirm it. OxygenOS now works flawlessly on my unit.

Thirdly, I will foray into root. Remember those four partitions? It's best to create backups of 'em. Although this backup is not necessary for rom conversion, I would still highly recommend making backups of which. Apparently, those dd commands require root. Are you afraid of entering point of no return after rooting? No worries, you can still go back to unrooted state and relock bootloader even on Oneplus 12, I have tried it myself on ColorOS. Let's say you have just rooted your Oneplus 12's ColorOS using magisk and you would like to go back to the default unrooted state, you just need to uninstall magisk app through the magisk app itself. Then you can proceed to flash the factory init_boot image before you flashed with a patched version. After that, head over to local install and toggle airplane mode(else the option will be greyed out), then install whichever your original rom was when it first came out of the box for 2 times if you want to ensure complete erasure of any trace of root before relocking bootloader. As far as I am concerned, do not simply relock bootloader if you are not entirely confident, do not proceed, you might risk bricking your device, better be safe than sorry. If you happen to be one of the folks who is wondering if relocking bootloader after rooting is possible, my answer is yes. If somewhere someplace there exists a CN set owner who happen to need to ship his unit back to China for warranty claim(be it LCD replacement etc), yes, relocking bootloader is required. You don't wanna gamble on the possibility of Oppo denying your warranty claim on grounds of bootloader tampering after you shipped it back to China half across the globe, don't listen to the naysayers who say otherwise. Refer to post #2 for more details. Also, remember to reflash ColorOS rom if you were to ship it back to China. Do note that both locking and unlocking of bootloader would result in data wipe.

Update: This is even better, you can backup the important images without rooting, I have not tried this myself, will keep forumers posted after I tried this myself. Thank you @EtherealRemnant

Since I can't find any tutorial on unrooting and relocking Oneplus 12 online, it took me a while and some unpleasant experience on a non-English unofficial chat messaging discussion group with smug, insufferable admin with superiority complex which I'd rather no go into detail (pm me if you are morbidly curious) but I figured out nonetheless.

If you happen to be OP12 owners of another regions in the same shoes as mine, I believe my third point will work for you as well with the respective adjustments, but I'm not entirely sure, I am not an expert.

Treat this thread as a casual Oneplus12 chat, cheers, AMA. Again, hope my thread helps, thanks.

*Do correct me if I am factually wrong.

Edit: added image backup image method without requiring root