How do I inject the info into the smbios.plist file?

How do I inject the info into the smbios.plist file?
I tried opening it with text editor but I cant save the changes I make due to permission rights. (I want to inject info about my cpu)

(Still says Intel Quad-Core Xeon for i5/i7 by default. However, you can inject i5/i7 info into About this Mac by inserting SMcputype into smbios.plist.

For i5, use 1537. For i7, use 1793 . Thanks to Lightspeed and zoleg! )

You'll need to copy it to the desktop (just drag it from /extra to there) before you can edit it, and then drag it back when finished.

This is a job for... a Mac guy

Right click the parent folder and select "Get Info". At the bottom of that box you'll see "Sharing and Permissions"... you don't have permission to edit the contents, but you can fix that. Click the lock, enter your admin password. Then click the plus sign, add yourself or all administrators to "Read". Finally, change Read to Read/Write. Now you can save changes to the files inside as usual.