gosd,
Once you rename your copied aircraft folder, change the name to what you want on the "title=" and "sim=" line in the aircraft config. Then change to that name dp file and air file, then in the MODEL folder open the model.cfg and change "normal=" to that same name, save it, and change the name of the mdl file to the same name.
Once you have renamed all of these files to the one you want, put the new aircraft back into your AIRCRAFT folder.
Now use Morton's utility, add the new plane, and select the mission and or campaign mission you want to change the aircraft in and merely change it using MK's utility.
This way, you only have to make changes to the new aircraft instead of hand editing the MIS files.
Also, by changing the name in all of the aircraft folders, (simply rename the folder then copy it and paste it into all of the files as stated above), you now have it listed in free flight as a different aircraft.
If you do not rename it in all of the locations I named, you have several aircraft with the same name and have to choose it from a list similar to an aircraft with many skins.
In other words:
I take a TBF_Avenger and rename it to TBF_Avenger_MkII_828.
In the AIRCRAFT cfg I change
[fltsim.0]
title=TBF_Avenger
sim=TBF_Avenger
TO
[fltsim.0]
title=TBF_Avenger_MkII_828 "HMS Implacable"
sim=TBF_Avenger_MkII_828
I change the TBF_Avenger AIR and DP to TBF_Avenger_MkII_828 AIR and DP.
In the MODEL folder I change the names from TBF_Avenger to TBF_Avenger_MkII_828 for both the MDL and inside the CFG file.
I now copy and paste that new aircraft: TBF_Avenger_MkII_828 into my AIRCRAFT folder and use Morton's "mk_cfs2_util" to add that aircraft to my CFS2 install, then change out the original player aircraft to the new one.
I then use Jonesoft QC editor to add it to my Quick Combat, "QUICKCOM" folder and qc_plane QCB file.
This sounds like a lot of editing work, but it is mostly copy and paste.
All names of the new aircraft have to agree or it doesn't work out so well, which is why I don't hand edit my mission files very often.
I let Morton's utility do that for me.