Well, I can try to describe what I did:
After I have made the changes in the .xsd file of my 2DS, I saved it. Then, when I want to close the .cab file of my form I am told that a file was changed since I extracted the file from my form and I am asked if I want to delete it to see the archive.
When I click 'No, I don't want to delete it', I cannot open the .xsd file again.
But when I press 'delete', I do not see my changes in the .xsd file of my 2DS.
Thus, I assume that my changes are not even saved.
Then, I am trying to open the manifest.xsf