Q:

Can't edit .plist in /System

I would like to edit the following plist file using XCode, so that I can change some screensaver effects.
/System/Library/PrivateFrameworks/Slideshows.framework/Versions/A/Resources/Content/EffectDescriptions.plist
However I get a message from XCode that I don't have permission to change this file.
So I try to change the permissions
sudo chmod 664 /System/Library/PrivateFrameworks/Slideshows.framework/Versions/A/Resources/Content/EffectDescriptions.plist
and I get this error
chmod: Unable to change file mode on /System/Library/PrivateFrameworks/Slideshows.framework/Versions/A/Resources/Content/EffectDescriptions.plist: Operation not permitted
I have given my Terminal "Full Disk Access" in system prefs. Now what should I try?

A:

/System is protected by SIP (System Integrity Protection), which prevents writes made there.
It can be disabled, but you might be better off seeing if you can make modifications some other way, e.g. creating a duplicate screensaver effect that is saved to /Library.
Catalina is already doubling-down on system alterations by placing the system on a read-only volume, so any changes you make will be short-lived.

