Enemy or Model Swap for Snakes?

Super easy to do!

You will need to download Raz0r's Companion DLL (which is part of the Trainer download). This will require a legitimate copy of the game that is launched through STEAM (this will not work for cracks). 

Once you place the dinput.cfg and the dinput.dll in your BIN32 folder, you'll need to create a directory in your game directory:
\Steam\steamapps\common\Resident Evil 4\FILES\STAGE\MAIN

In the 'MAIN' folder you will need to create a .txt file called 'enemy_swap.ini' (just create a .txt file and rename the extension to .ini)

Next, edit the file to read:

[ENEMY_SWAP_GROUP_0]
enemy = 0x24
outfit = 0x0
health = 0
replace_with = 0xXX
replace_outfit_with = 0x0
replace_health_with = 1000
count = 100

Where XX is you will need to put an enemy ID so swap out with the snake. Y0u could use 12, 13, 15 etc for Ganados. There is a list of enemy IDs listed on this site HERE. 

The way this works is that whatever is loaded into the STAGE\MAIN\ directory will get loaded for EVERY ROOM IN THE GAME.  I don't know if this will create enemy compatibility issues but it is a possibility. What I mean by this is that some enemies simply wont spawn if there are certain combinations of them. To avoid this there is another way to go about using the enemy_swap.ini file:

Otherwise to do it room by room you could copy that newly created .ini file into room folders you could create in the  'MAIN' directory. It would look like this:

\Steam\steamapps\common\Resident Evil 4\FILES\STAGE\MAIN\r100
\Steam\steamapps\common\Resident Evil 4\FILES\STAGE\MAIN\r101
\Steam\steamapps\common\Resident Evil 4\FILES\STAGE\MAIN\r102
\Steam\steamapps\common\Resident Evil 4\FILES\STAGE\MAIN\r103 etc... 

Placing the enemy_swap.ini file in each of the individual room folders would give you more control over what enemies get swapped in the various rooms (you could basically edit each file to your liking). If there are compatibility issues with just using the one file in the 'MAIN' folder, then your best bet is to use the individual room folders. THere are actually more complex setups to create more variety in what enemies will swap out for the snakes, but I guess I would at this point then invite kTeo to fill you in on those details, as I am relatively new to using this feature of the Companion DLL. 

I really hope your friend gets over their phobia of snakes, as the likelihood of actually being bitten by one are very low. Irrational fears spilling out into video games doesn't seem like a healthy disposition. 

Best of Luck, and.....

Happy Modding!