We haven't yet implemented a way to change the type of a folder and, to my knowledge, no one has ever requested it before, but I can see that in your case it's sorely needed. I'm going to add a feature request for it.
There is a workaround, though. You can do it using an SQL command that can be executed from the command-line, as follows:
1. Stop the CompleteFTP service
2. Open a console
3. Change into the directory C:\Program Files (x86)\Complete FTP\Server
4. Execute the command cftpconfig.exe /q "UPDATE Node SET NodeTypeID='7da9861c-271e-4cf5-b35d-aff10f6042e5' WHERE NodeID='cf60f079-0747-47e4-bc9f-ff3460134be8';"
5. Restart the service
You should now find that the type of the /Home folder has changed to Network/Macro Folder, which means that you can edit it as text and enter the UNC path as required.
You should find that the change propagates to the secondaries in your cluster upon start-up, but if you find that they don't then you can force synchronization to make sure that they have.
Does that help?