ivancito_1 wrote on Oct 31^st, 2012 at 4:47pm:

The probable reason for why you can't edit and save the aircraft.cfg is because FSX is installed in the default location (Vista/Win7) C:\Program Files or C:\Program Files (x86).

I think that what others do, to get around that problem (so correct me if I'm wrong), is this:
1. BACKUP THE AIRCRAFT.CFG BEFORE YOU START EDITING IT, in case you make a mistake (if you haven't already done so).
2. Copy the aircraft.cfg and paste it on the desktop.
3. Open it with Windows Notepad.
4. Add the details needed for the new livery ([fltsim.xx] etc.)
5. Save the changes.
6. Copy the edited aircraft.cfg and paste it back in the CS_B767-XXX folder and allow it to overwrite (replace) the original aircraft.cfg.

It is for reasons like this, that it is not recommended to install FSX in its default location if your operating system is Vista or Win7

Hope this helps.