You'll need to set the launcher to run as admin.
To do this, open windows explorer and navigate to your MW directory, right click on the Morrowind launcher.exe, click the compatibility tab at the top, then check the box that says run as administrator. You'll need to do this for the Morrowind.exe too. Then you should be able to start the launcher, click the data files, and uncheck the MCA 6.1.esm. After that's done, use the technique from the previous post (save in an unmodded area, etc.) to make a clean save. It should be enough to do what you need.
KF