Blimey, it has been that long since I fiddled around in the editor, I have forgotten the ins and outs of it. I just had a quick play around, and I got into advanced rules for the FCWC by doing this.
Once editor loaded, in Database tab, click Competition and select FCWC
Then change the Nation to Spain (for this example)
Add Nation (eg Spain)
Click Add Lower Divisions And Cups to Existing Structure
Convert To Advanced Rules
In List, you will now see all the Spanish competitions plus the FCWC (there are 2 entries in FM22)
Remove all the Spanish competitons leaving just the FCWC file you want to edit
Remember to remove the nation and Continent from the database entry of the FCWC that you changed at the start.
Save the file and you should now have advanced rules access to the FCWC for you to change what you need to
Good Luck.