We need to create the following files and folders

1. ..\My Documents\Paradox Interactive\Crusader Kings II\mod\CoA.mod

name = "CoA"
path = "mod/CoA"

2. ..\My Documents\Paradox Interactive\Crusader Kings II\mod\CoA\gfx\coats_of_arms\pattern_x.tga

To make it easier. Get ready file and rename it .

Copy ..\Steam\SteamApps\common\Crusader Kings II\gfx\coats_of_arms\patricians.tga -> ..\My Documents\Paradox Interactive\Crusader Kings II\mod\CoA\gfx\coats_of_arms\pattern_x.tga

On top of old coats of arms imposes new coats of arms . Each coat should be the format of 128 x 128 tga.

3. Now you need to register a new file pattern_x.tga in coats_of_arms.txt .

Copy ..\Steam\SteamApps\common\Crusader Kings II\interface\coats_of_arms.txt -> ..\My Documents\Paradox Interactive\Crusader Kings II\mod\CoA\interface\coats_of_arms.txt

Find
texture = {
file = "gfx\\coats_of_arms\\dynasties4.tga"
size = { x = 16 y = 4 }
noOfFrames = 52
color = 0
random = no # Do not use for random CoAs
}

And add your text after it

texture = {
file = "gfx\\coats_of_arms\\pattern_x.tga"
size = { x = 16 y = 2 }
noOfFrames = 25
color = 0
random = no # Do not use for random CoAs
}

Here
16 - the number of coats of arms in one line
2 - the number of rows with your coat of arms
25 - the total number of coats of arms in the file

4. Now you can now specify a coat of arms to use for each of the vassals in your county.

Copy ..\Steam\SteamApps\common\Crusader Kings II\common\landed_titles\landed_titles.txt -> ..\My Documents\Paradox Interactive\Crusader Kings II\mod\CoA\common\landed_titles\landed_titles.txt

eg

Open file, find the rows

b_klin = {
}

and replace its

b_klin= {
coat_of_arms=
{
data=
{ 0 9 0 2 0 0 0 }
religion="orthodox"
}

where
0 - Template (Used only plain)
9 - The pattern texture file ID to use. (The game is already present eight , our ninth)
0 - An optional tag setting the emblem ID to draw on the layer (not used)
2 - The ID of the pattern tile in the file to use (0 - first, 1 -second, etc)
below is color, not used here
0 -
0 -
0 -

religion must be specified . This is an indication of how the program set to be used .
see also
http://www.ckiiwiki.com/Coats_of_arms_modding