It entirely depends on the race you're playing on (or whatever race you're viewing yourself on, if using plastic surgeon, keep in mind).
Here's a basic rundown on what you have to do:
1. Locate the Uriel Blade file for the Race/Gender you want, copy it
2. Paste it to your desktop, so you can change it's name without interfering with the rest of your files
3. Change the filename to the number listed below for the SAVAGE BLADE filename that matches your race/gender. For example, if you were playing on Hume male, change the file from 3.dat to 19.dat
4. Locate the actual Savage Blade file, and rename it to something like 19old.dat so you don't lose it, and can change it back if you want to later
5. Copy the renamed Uriel Blade file into this folder
You will notice the effect on WS .dat swaps after you zone, I believe.
Easy, right?
All FFXI .dat files are located on your computer in the following folder (this is assuming you installed at the default locations):
C:\Program Files (x86)\PlayOnline\SquareEnix\FINAL FANTASY XI\ROM
From here, there's a LOT of folders simply titled with numbers. When I reference files below, i'll say, for example, "240/19". This refers to the folder numbered 240, and the file within called 19.
File locations for the following races. Uriel Blade (UB) followed by Savage Blade (SB):
Hume Male: UB - 240/3 | SB - 100/19
Hume Female: UB - 240/10 | SB - 101/48
Elv Male: UB - 240/60 | SB - 102/77
Elv Female: UB - 240/24 | SB - 103/106
Tarutaru (both genders): UB - 240/32 | SB - 105/7
Mithra: UB - 240/39 | SB - 106/36
Galka: UB - 240/48 | SB - 107/65
If you want to do more .dat swapping, I recommend downloading a program called "Altanaviewer", just do a Google search and you should be able to find it. This allows you to browse all gear and animations in the game, giving you the source file name. You can then swap them around any way that you like (want to use Fudo's animation for your Exenterator Weaponskill? Maybe Asuran Fists instead of Resolution? Like we could stop you!)