How do I unlock a .plist file in /private/var/db/receipts so that I can change it? I want to edit some com.myApp.plist. I'm running OS 10.10.3, and I do have Xcode installed. But every time I try to edit the file, it's locked and I can't save my changes.

If I try to save it with Xcode, Xcode asks if I want to unlock it. I say "Unlock", but then an error says The file "com.myApp.plist" could not be unlocked."; it says that this is because I do not own it.

If I open the file in Sublime Text, its just the object code. 

How can I make changes to the file? 

I have tried sudo chown $USER com.myApp.plist followed by sudo chmod u+w com.myApp.plist. They both succeed but I still can't edit the file.

I have tried using Finder to change each folder in the path to add me as a read/write user, but still no editing capability.

I have tried opening the file from Terminal using sudo com.myApp.plist which opens Xcode. Doesn't work.

Not sure what else to do. I could try something like "apply to enclosing folders" but that seems dangerous.
You probably need to add an ACL to the immediately enclosing folder too. 

Not certain about the entire path, but you could always later remove with
sudo chmod -R -N /path… at the highest directory level you reached to enable it, which will remove ACLs from the entire directory tree at &amp; below your /path...