I was about to make a patch updater for a couple of friends, and I realized it might be useful to someone else. It is for running from Windows (tested to be ok in Win10 Pro).
It covers steps 2 and 3 of the original post instructions, WITH THE EXCEPTION OF THE DOSBOX CONFIG FILE MODIFICATION, that you have to do yourself.
The zip file contains a .txt file with the VirusTotal scan link and the SHA-512 checksum for an .exe file made with a free patch creator program (so, sorry for the plug at the end of installation, but it really is no big deal).
This is a patch, no complete game files are contained in the updater, only 'resource.cfg' and 'krondor.cfg', since they could have been changed by the user if they run the configuration or the game itself before running the update.
Download link: http://www.mediafire.com/file/dbt7p4c87a4kvm1/BaK_update_redux_by_Links_for_GOG_release.zip
I also made one for the Sierra 1.02 Free Release, but I doubt it will be useful for anyone here. That one includes the changes made by the official patch, since Sierra messed up back then, and did not include all the fixes of the original 1.02 version.