Hi, sorry if I'm late on this one.

I usually do more or less do the following:

1. Duplicate FileA.idf
2. Open FileA-duplicate.idf in SketchUp, accept the loss of information and make the changes.
3. Upgrade FileA-duplicate.idf to 9.0
4. Pass both files through the IDFFileEditor.exe to re-order the syntax.
5. Open both files using a diff comparator (vimdiff, FileMerge, ...), and copy/replace everything related to both geometry and zones from FileA-duplicate.idf to FileA.idf.