I had to uninstall and re-install TW2 just to get the patch to install properly, but when I entered my registration information to unlock the Downloadable Content menu, my Pre-Order DLC wasn't there (But the Polish VO and text language packs were....). I tried reentering the codes, but got "Invalid Code" errors, and then I saw at the bottom of the DLC info card that there are code revocation instructions (it also says I can install my DLC on up to five PCs, so I should at least have been able to use the code again, even if I hadn't previously revoked an old redemption). It says "Use the same process as above (referring to the redemption process) , but enter your code in the 'Code Revocation' box instead".

Is that fix universal? Or is it only for the GoG or other "digital" versions?

It's universal. It basically installs the DLC for you.

Though there's one caveat. The developers advise to install patch 1.1 before attempting to install the DLC via those installers.

Well, as I said, I just re-installed the game, and so it auto-downloaded and installed the patch. What I'm really worried about is getting my game "bricked" if CDPR decide later to re-implement DRM on the pre-order DLC, and I haven't properly registered it. The post on the official announcement page says it's "a temporary fix until further notice".

Once you have the items in a saved game, disabling the DLC shouldn't remove them.

Though I'm certain they made all the DLC free due to the patch 1.1 delay fiasco.

I don't think that's the sole reason they would make all packs free, but it would certainly be too late/take too much effort to try restricting them now.