If your sim has been installed in it's default location & you are having config editing issues, you do not have to uninstall & then re-instal!
Simple.. to make it easier, i use a copy program from
https://www.codesector.com/teracopy called teracopy.
It is probably the fastest copy program out there.
So, optionally download & install that
Then, go to your Microsoft Games folder in C:\Program Files (X86), it probably is there, & copy the whole ' Flight Simulator 9' folder
then, go to your C:\ drive, & paste it there.
DO NOT RUN YET.
Now for the 'delicate part' ...
Rename the newly pasted folder to 'Flight Simulator 91' for example.
Open that folder & rename the FS9.exe to FS91.exe,
Right click that & send to desktop.
You now have a new icon on your desktop for a second version of Flightsim 9.
Now run it!
You most probably have to activate your add-on scenery again.
Then, go to
https://www.flight1.com/view.asp?page=library & download the Registry Repair tool, run that & select tyhe FS2004 option.
ALL should be good.
IF you do have any start up issues after all this, Right click the desktop icon, Select compatibility mode & select Windows XP, then, below that, Run as Admin.
It almost is quicker to do than to explain.
Using this method, you can have multiple versions of FS2004, remembering to rename the main folder & exe every time.
I have 3 different versions, a 'normal' version, a Golden Wings version & a Ford Tri-motor Project version, each with different scenery & planes.
I hope I have not confuddled you
All the best,
Robin
Cape Town, South Africa