Once a game is started which data files can be updated for games in progress assuming both players update the same file?
This one is a real witch, but bear with me. If anything isn't clear, please feel free to ask.
The Basis files (the ones that are used/selected in other files) are "Mostly" ok to update - Devices, Classes, Airplanes. But ... Even with these files, "Some" of the data values that are used to configure on-the-board units or ships or whatever, should not be changed for ongoing games. Here's some examples that hopefully make it clearer.
One can change the DATA fields in a Device file and have things update cleanly. That's because the devices in a LCU or Class file are just pointers to a Device slot number. The pointer don't care what the data is, just where the slot number is. The program will consult the requisite data values when they are needed, but nothing on-the-board requires them to be held somewhere, so no worries about these.
"Some" changes to the DATA fields in a Class file will update cleanly. Note .. the Class file data fields are the green ones, on top, NOT the Wpn listings. "Some" of the data fields are used for savegame purposes for on-the-board ships that refer to that Class; Ships in port, or in repair, or such like, have things calculated in terms of their Tonnage. Dinking with that will cause vomiting by the load/unload and repair algorithms if things change in midstream. Same with cargo caps; if an on-the-board ship (or ships) are loaded to one cap level, then changing the cap level in midstream will cause vomiting and perhaps loss of troops and other stuff into a virtual black hole.
"Some" changes to the DATA fields in the Airplane file will update cleanly. NOT the Wpn listings, but the data stats. So Maneuver (for example) should be ok since there is no other place it is saved for on-board stuff in a savegame.