Okay, I have some information that someone may find useful.
Tried this with XCOM Editor v1.3, v1.4, v1.5, and v1.6.
It does work, and quite well - thank you - with Microsoft .NET Framework 4.5.
HOWEVER, it doesn't work with all saves.
When I decompress the save file data, I get a different number of "Blocks" with different saves. On saves where there were more than 10 blocks decompressed, the editor couldn't open them. But, on saves with, say only 6 blocks, it opened them just fine and I was able to edit, save, compress, replace, rehash, resign, and everything loaded up and played just fine.
Of course, the save that I really want to edit has 43 blocks. . .
Anybody have any ideas?
Thanks.