@DeViL303 Dummies shouldn't be empty files. For best compatibility (we never know what kind of security checks developers was add) they should be header for target replacement + void (1s of black video, 1s of silence etc.). Of course it is often sufficient but I have trauma from PS2 time.

Sick bastards making crazy sec those times.
@lmn7 As I remember, mM called it "Shadow Copy".
@x23are You should know that You risking destroying fs table "if something goes wrong".
In general, you can use 0kb empty files... and with this i meant for any file that is not going to be loaded by the game (as example, there could be files with custom file extensions that are repeated "by language")
Also, following this same rule you can replace any other file that is not going to be loaded, as example, the mutiplayer maps of a game just because you are not interested in playing in multiplayer, or because the game servers are already closed
What you was mentioning happens with videos... but only with the videos that are going to be played (lol, i know im repeating myself but this is a key concept to remember)
Im going to show you an example from the game killzone 2 (i played it past week and ripped it too a bit, this game is a nice candidate to be ripped btw, it has lot of video "garbage")
The first video files that can be deleted are the intro videos for each language (there are 16, around 200mb each), and you only need to keep 1
Next videos that i ripped are the ones that appears on the "press start" screen (only after some minutes of inactivity in the dualshock, the game starts a loop sequence where are played 6 videos)
Some of that "press start" videos are duplicateds, you have a version where the KILLZONE2 logo have a "trademark" charater, and the other version have a "registered" character (lol, yeah is retarded)... i guess are intended to be played by region
I noticed when i was booting the game it was using the "registered" everywhere (for all europe regions i guess), so i deleted the others with the "trademark"
Later i realized (by renaming one of them) that the video player of the "press start" screen it was not crashing when it was trying to play a "missing" video... so i deleted all them (are the files named Attrac*.avi)
Anyway, i just kept the video of the intro (with a nazi like speech of the supervillain) but the reason why i decided to delete them is because in this game the video player doesnt crashes if the video is missing
But as a general rule... is needed to do what you said

To replace a video file is needed to use another video file with the same exact format (but only containing a few frames in black)
This way the game can actually play the video normally... is just you only see on screen a "poof" with a black frame (faster than a second, is mostly like an interference)
I never remove of replace the "ingame videos" neither the intro... but this is handy to remove the "press start" videos i mentioned (and also the "how it was made" extra videos from some triple AAA games like dunno, god of war, heavy rain, uncharted, etc...)
*Funny fact... the game KILLZONE2 have a "dummy.avi" video you can use to replace the others (and you can play them in PC btw, this "dummy.avi" is an audio test used in development)
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Also, keep in mind all this experiments needs to be tested before giving your rip the "quality control passed" label
For it is needed to uninstall the gamedata... and install it again (because sometimes that gamedata instalaltion is going to do something with the files you have been modifying)
I use to unstall the savedta too just incase (most games creates and loads savedata automatically in every boot)