To do it with JSGME, you'd need to create a mod for it with the proper file structure.
Main folder: name of mod (Intro TGA or whatever you want to call it)
This main folder would be the one that gets copied into your game's MODS directory.
Inside the main folder, a folder named
data and inside that the same folder structure as the game's
data subfolder, but you only need the folders/subfolders that the relevant file is in. Mimic that file structure until you get down to the subfolder that contains the file you want to swap in and out. In that folder, put the version of the file that you want to use.
When JSGME enables the mod, it will look at the mod's file structure and follow the folder/subfolder path you created down to where the file is, and put the new file in the same location in the game directory (while also removing and creating a back up of the file that's already there).
If you have other mods that you're using with JSGME, you can click through their file structure to see the way they're set up and the way it mimics the file structure of the game directory. I would tell you which folders/subfolders you need to create but I don't have the game reinstalled yet, so no game directory to refer to on my end. Someone else will no doubt be able to provide the specific info if necessary.
