I’m afraid this isn’t as easy as it appears. There are two different approaches, as you identified, editing the ODF, and editing the CODM.
First of all, if the ODF of the organ you want to encode your voicing changes is copy protected, you will not be able to edit the ODF. If the ODF is not copy protected, you can concretize your voicing changes, but it is not recommended. The reason is that now you will have two different copies of the ODF that will behave very differently, but will for all other purposes look identical. Getting these mixed up is very easy. Al Morse made a program that helped do this, but without that program, it’s pretty tricky to translate your voicing into the parameters that the ODF recognizes. Not sure if that program is still available, and I certainly wouldn’t be able to tell you what parameters to edit.
As for editing the CODM, the only way to do this is to make a new custom organ that is identical to the organ you are wanting to modify, and make the desired voicing changes to the CODM file. That will then generate an ODF where the changes are permanent. The advantage of doing this is that you can use a different organ ID, so different versions will not overwrite each other. The disadvantage is that the starting point may not be the same, though if you are diligent with programming your CODM file it will probably sound pretty close to the same.
That all being said, the best is to save your voicing changes, and back them up using Hauptwerk’s back up utility, and keep that somewhere safe. In my opinion, that is the best option.