Hey Trasher and bjorn, thanks for the assist (I'm the girlfriend in question).
Thought I'd let you know how my alternative solution worked out.
Reading bjorn's response, it seemed to me that since Shifter changes the *.int file, and since Revison just copies, renames and appends to whatever *.int file is there, that if I just installed Shifter first, the Shifter *.int would be the one copied, renamed and appended to.
So that's what I did, and it appears to have been perfectly successful, with one minor issue.
In-game, naturally the title and so forth were changed to reflect Revision-- the first run, that little message saying welcome to Revision, enjoy! was a nice confirmation that Revision was in fact running (even after the splash screen and the fact that I was running Revision.exe rather than Deus Ex.exe), before I had moved to see anything different about the map itself. Under the main menu, some inserted text notes 'Shifter v. 1.8.3', so I also have confirmation that Shifter is running before I move into the map and see any new or changed items.
Further into the first map (I love Liberty Island, actually ), it's easy to see the Revision changes to the map, and after you kill/disable a few NSF, it's easy to see that Shifter is also working (having a stack of 6 Combat Knives is a big tipoff). I haven't yet tried the Shifter-added Alt-Fire key to throw them, but the Shifter-added button assignment is there in the *.rev file to do that, so it should all work fine.
The only issue I encountered 'behind the scenes' was that the last two groups from the Shifter *.int file got cut off when copied to the *.rev file. I haven't done a detailed diff between the two files to check if anything else got mangled in some way, but a moderately attentive manual scan of the two files didn't seem to have any major losses other than that.
The two 'lost' groups aren't important, really (a second copy of the IFF Augmentation description for some reason, and an email from Paul that probably refers to a unique Shifter item found in his appartment), but I copied them from the *.int file and appended them to the end of the *.rev file and am playing through to see if it will work (which it seems like it should, unless there's some kind of a file size or line/character limit attached to the *.rev file or something).
Otherwise, so far (of course, I'm still clearing Liberty Island, so I haven't got far at all in this 'new-style' game) all elements of both Revision and Shifter seem to be working as expected via the (even simpler) expedient of installing Shifter first, so that its *.int file, rather than the default, is the one copied to the *.rev file.
And for those interested, you may also be glad to hear that this whole process (both the installation, and the modified game itself) appear to be working so perfectly under Wine in Linux (since that's where I'm doing all this ).
Thanks again for your help, and for the mod-- it's a bit tough, but I'm enjoying it very much so far. Can't wait to get to Hell's Kitchen and see what's going on on those rooftops....