I decided to throw together a little guide after including a more race-specific one in my TaF->NiF race swap thread. I'll be changing my tauren female's scale so that my TaF to NiF race conversion will look better. For some reason when I packed my sizefix together with my modelchange it crashed people (maybe a localization thing?), so I wanted to share how I did it myself.
You'll need MyWarcraftStudio and DBC Editor.
[1] Open MyWarcraftStudio, go into WorldofWarcraft\Data\enUS\patch-enUS.MPQ. If you're not from the US it will be named with your localization.
[2] In patch-enUS.MPQ, you'll want to expand the DBFilesClient folder and search for CreatureDisplayInfo.dbc. Select this file, right click, and hit Extract to (somewhere you'll find it easily).
[3] Run DBC Editor now, click the open folder, and search for your extracted CreatureDisplayInfo.dbc. Open it.
On the leftmost side is an id column. These are the ids for all the race/genders:
The only thing you'll need to change here is YOUR original race/gender's field4 column. I'm trying to make my Tauren Female to NE Female conversion look smaller and more like an NE. The Tauren female ID is 60. Look over to the field4 column. These are the scales of the models. ID 60 has a 1 in the field4 column (100%). Through trial and error I figured out that the model needs to be scaled down to .8 (80%) for the TaF->NiF model conversion to be the right size for an NE.
49 - Human Male
53 - Dwarf Male
55 - NightElf Male
1563 - Gnome Male
16125 - Draenei Male
50 - Human Female
54 - Dwarf Female
56 - NightElf Female
1564 - Gnome Female
16126 - Draenei Female
51 - Orc Male
57 - Undead Male
59 - Tauren Male
1478 - Troll Male
15476 - BloodElf Male
52 - Orc Female
58 - Undead Female
60 - Tauren Female
1479 - Troll Female
15475 - BloodElf Female
IMPORTANT: There's no fixed size for each race. Both the NE Female and Tauren Female have 1 (100%) in their field4 column. Only through testing and playing with different percents and logging on and comparing my size to an actual NE npc/player could I find the right %. YOU'LL NEED TO DO THIS FOR ANY OTHER MODEL CHANGE'S SIZE FIX.
[4] Sure of myself that this scale would make my NE conversion perfect, I click the 1 in id 60, field4 column ONCE to change the number. I Type .8 in its place, then press ENTER. The highlighted space will go down one of you did it correctly. Now, save it and close.
[5] Open MyWarcraftStudio again. Go to Pack(P) -> Create MPQ archive. Name it patch-s or something. Go back to Pack(P) and click add file to archive. Select your edited CreatureDisplayInfo.dbc. An "Input the pathname of file to be" window will pop up with just CreatureDisplayInfo.dbc in it, rename it to DBFilesClient\CreatureDisplayInfo.dbc and press ok.
[6] You've got your sizefix mpq now. Move this to your data folder and make sure the .MPQ part is capitalized. Use it along with the original race swap, and your size should be fixed.
If you find the right field4 # for your race conversion's sizefix, post it and I'll make a list for others.