One thing I never asked - you are logged into the recorder with the user "admin" aren't you as that is required? If you are:
1 - So although they are uneditable directly on the NVR, you DID manage to already change the IP address. You should therefore be able to edit those fields by connecting to it using the browser (as you did before when you accidentally copied the wrong ones in) - so try that first.
2 - If you can't change them from the browser, by all means edit the gateway in SADP as you have mentioned - that should also work.
3 - The query regarding the Wizard - you could see if it lets you edit the settings there. I don't use it and always untick the box for show wizard at startup.
4 - If all of the above fails and you're still unable to edit that field by any means, the firmware or configuration may be corrupt. As a first step I'd refresh the firmware onto the NVR. It's not as daunting as it sounds. There is no newer version available for your NVR than the one you already have; However if you download the file and run the update, it should just install the same version over the top of the existing without affecting any other settings. Here is the link to the correct firmware file fr your NVR:
www.hikvisioneurope.com
As you're on a Mac it will unzip itself automatically and appear in the Downloads folder as "digicap.dav". Using Safari, go to the IP address of the NVR then go to Configuration > System > Maintenance. At the bottom of the page beneath Upgrade click browse and navigate to the digicap.dav file in your Downloads folder, then click Upgrade. It'll take a few minutes and when complete the NVR will reboot. Hopefully that will resolve it and you can edit away.
5 - The nuclear option. If everything else has failed and it still can't be edited either locally or using the browser - go to back to Configurations > Maintenance and click the Default button. That will wipe all settings including the IP address before rebooting it again. You would then use the local menu on the monitor to set it back up using the wizard or manually.