I have two Grand Chancellorville modules. This game is a combination of Fredericksburg and Hooker and Lee, a la Napoleon’s Last Battles. I have one module that was converted from an ADC 2 OPS file. It opens up with the units on the map, but it is very incomplete. The second module has the Hooker and Lee maps from the two SPI games electronically pasted with no units on the map. I like the ADC map better than the SPI paste job. Is it possible to swap maps, and if so, how can it be done?
Well, if you’re ready to “get your hands dirty” with a little bit of Vassal Module editing, you could try these steps:
(1) Make a backup of both modules - heh!
(2) The one you want to grab the map from (ADC?), rename the .vmod file to .zip (Vmod files are really just zips in disguise)
(3) Now open the Zip in any way you’d normally open a Zip (on windows you can just browse in like a directory)
(4) There will be a subdirectory “images” – go into that
(5) Somewhere in here is the map file (along with every other image in the module). Find it and pull it out to a regular non-zip folder (really you could just pull all the files out somewhere, and then they will be easier to look through w/ thumbnails and stuff).
(6) Now, go into Vassal and select Edit Module on the one you want to add the map to.
(7) In the list of things in the editor window, look for the entry for “Main Map” (or “Map”). Open that up. Inside that the top entry is usually an entry “Map Boards”. Open THAT, and there will be an entry for a specific board (e.g. “Map [Board]”) – this one you want to double-click or right-click-and-pick-“Properties” on.
(8) Press the “Select” button next to the Board Image.
(9) Browse to the folder you put the cool ADC map and select it.
(10) Press okay and stuff.
(11) SAVE the module
(12) Exit completely from editing the module
(13) Now, open the module again (either for Edit or for Open is fine, for your experiment) and try to start a game.
(14) You should see the ADC map in the module!
Now, if you turn out to be The Luckiest Human Being In The Whole World, then not only will you see the map but it will have turned out to be a pixel-perfect replacement image for the old map, i.e. exactly the same size, shape, etc, and you’ll be done.
MUCH more likely is the map turns out to be a different size, and things are suddenly “in the wrong place” and stuff like that. This will then begin steps 15-1000 aka “Your Brand New Career Editing Vassal Modules”!!! 
Look, it’s how I got started back in November, “I just wanted to fix one thing”, hahahahahahaha! Anyway, if you end up needing to do fixes, then the first fixes are likely to be further into that “Map [Board]” I showed you earlier, you’ll have to get the grid/locations/zones all lined up to the new map. Then you’ll be off looking for At Start stacks and getting them moved to the right locations, etc, etc, etc. It’s totally do-able, you’ll just learn it bit by bit as you go…
Good luck!
Brian
After step 5 I would suggest using the same method to extract the SPI based map, then using photoshop/gimp to rescale the ADC based map so that the ADC hexes are exactly the same dimensions/relative location (easy enough, but feel free to PM me if you want it done for you). This will save you the disappointment and suffering of step 15.